tài liệu dạy học

ảnh ngẫu nhiên

Menu chức năng

Các ý kiến mới nhất

Điều tra ý kiến

Bạn thấy trang này như thế nào?
Đẹp
Bình thường
Đơn điệu
Ý kiến khác

Thành viên trực tuyến

1 khách và 0 thành viên

Thống kê

  • truy cập   (chi tiết)
    trong hôm nay
  • lượt xem
    trong hôm nay
  • thành viên
  • Bác Hồ Đọc Tuyên Ngôn Độc Lập

    Anh Kim Đồng

    Toán 4 tập 2

    Wait
    • Begin_button
    • Prev_button
    • Play_button
    • Stop_button
    • Next_button
    • End_button
    • 0 / 0
    • Loading_status
    Nhấn vào đây để tải về
    Báo tài liệu có sai sót
    Nhắn tin cho tác giả
    (Tài liệu chưa được thẩm định)
    Nguồn:
    Người gửi: Hoàng Việt Hưng
    Ngày gửi: 14h:23' 12-11-2025
    Dung lượng: 11.9 MB
    Số lượt tải: 0
    Số lượt thích: 0 người
    HÀ HUY KHOÁI (Tổng Chủ biên)
    LÊ ANH VINH (Chủ biên)
    NGUYỄN ÁNG – VŨ VĂN DƯƠNG – NGUYỄN MINH HẢI
    HOÀNG QUẾ HƯỜNG – BÙI BÁ MẠNH

    TOÁN 4
    TẬP HAI

    NHÀ XUẤT BẢN GIÁO DỤC VIỆT NAM

    SÁCH GIÁO KHOA ĐƯỢC THẨM ĐỊNH BỞI HỘI ĐỒNG QUỐC GIA
    THẨM ĐỊNH SÁCH GIÁO KHOA LỚP 4
    (theo Quyết định số 1908/QĐ-BGDĐT ngày 11 tháng 7 năm 2022
    của Bộ trưởng Bộ Giáo dục và Đào tạo)

    HÀ HUY KHOÁI (Tổng Chủ biên)
    LÊ ANH VINH (Chủ biên)
    NGUYỄN ÁNG – VŨ VĂN DƯƠNG
    NGUYỄN MINH HẢI – HOÀNG QUẾ HƯỜNG – BÙI BÁ MẠNH

    TOÁN 4

    TẬP HAI

    (Bản in thử)

    NHÀ XUẤT BẢN GIÁO DỤC VIỆT NAM

    MỤC LỤC
    Chủ ề
    8

    9

    10

    2

    Nội dung

    Trang

    PHÉP NHÂN VÀ PHÉP CHIA

    4

    %ÃL1KÅQYĸLVŪFÖPŮWFKŅVŪ

    4

    %ÃL&KLDFKRVŪFÖPŮWFKŅVŪ

    6

    %ÃL7ÐQKFKŖWJLDRKRÄQYÃNŠWKļSFĦDSKÌSQKÅQ

    9

    %ÃL1KÅQFKLDYĸLh

    14

    %ÃL7ÐQKFKŖWSKÅQSKŪLFĦDSKÌSQKÅQîŪLYĸLSKÌSFŮQJ

    17

    %ÃL1KÅQYĸLVŪFÖKDLFKŅVŪ

    20

    %ÃL&KLDFKRVŪFÖKDLFKŅVŪ

    23

    %ÃL7KņFKÃQKYÃWUþLQJKLŤPòĸFOòļQJWURQJWÐQKWRÄQ

    27

    %ÃL7ÏPVŪWUXQJEÏQKFŮQJ

    29

    %ÃL%ÃLWRÄQOLÍQTXDQîŠQUÝWYšîðQYĞ

    31

    %ÃL/X\ŤQWŚSFKXQJ

    33

    /£048(19Ľ,<ť87ů7+ů1*.­;¤&68ś7

    36

    %ÃL'Æ\VŪOLŤXWKŪQJNÍ

    36

    %ÃL%LŢXîūFŮW

    39

    %ÃL6ŪOŗQ[XŖWKLŤQFĦDPŮWVņNLŤQ

    43

    %ÃL/X\ŤQWŚSFKXQJ

    47

    3+¥16ů

    49

    %ÃL.KÄLQLŤPSKÅQVŪ

    49

    %ÃL3KÅQVŪYÃSKÌSFKLDVŪWņQKLÍQ

    52

    %ÃL7ÐQKFKŖWFðEþQFĦDSKÅQVŪ

    56

    %ÃL5ÝWJĔQSKÅQVŪ

    59

    %ÃL4X\îūQJPřXVŪFÄFSKÅQVŪ

    62

    %ÃL6RVÄQKSKÅQVŪ

    64

    %ÃL/X\ŤQWŚSFKXQJ

    69

    Chủ ề
    11

    12

    13

    Nội dung

    Trang

    3+¬3&ų1*3+¬375ň3+¥16ů

    74

    %ÃL3KÌSFŮQJSKÅQVŪ

    74

    %ÃL3KÌSWUŃSKÅQVŪ

    80

    %ÃL/X\ŤQWŚSFKXQJ

    83

    3+¬31+¥13+¬3&+,$3+¥16ů

    86

    %ÃL3KÌSQKÅQSKÅQVŪ

    86

    %ÃL3KÌSFKLDSKÅQVŪ

    91

    %ÃL7ÏPSKÅQVŪFĦDPŮWVŪ

    95

    %ÃL/X\ŤQWŚSFKXQJ

    98

    ·17ş3&8ů,1õ0

    102

    %ÃL·QWŚSVŪWņQKLÍQ

    102

    %ÃL·QWŚSSKÌSWÐQKYĸLVŪWņQKLÍQ

    105

    %ÃL·QWŚSSKÅQVŪ

    107

    %ÃL·QWŚSSKÌSWÐQKYĸLSKÅQVŪ

    110

    %ÃL·QWŚSKÏQKKĔFYÃîROòĹQJ

    112

    %ÃL·QWŚSPŮWVŪ\ŠXWŪWKŪQJNÍYÃ[ÄFVXŖW

    114

    %ÃL·QWŚSFKXQJ

    116

    0ŮWVŪWKXŚWQJŅGÜQJWURQJVÄFK

    119

    +Æ\EþRTXþQJLŅJÏQVÄFKJLÄRNKRDîŢGÃQKWŐQJ
    FÄFHPKĔFVLQKOĸSVDX

    3

    Chủề

    8

    Bài 38

    PHÉP NHÂN VÀ PHÉP CHIA

    1+19ƈ,6ž&0Ɔ7&+Ɯ6ž
    7URQJQJj\QKjPi\ÿy
    V̻Q[X̽Wÿ́ͻFEDRQKLrX
    FKL͗FNḰXWUDQJQK͡"

    KKÀPSKÀ
    0ͯLQJj\QKjPi\
    V̻Q[X̽Wÿ́ͻF
    FKL͗F
    NḰXWUDQJ

    160 140 × 7 = ?

    7KΉFKL͟QẂ˿QJWΉ
    QḰSKpSQKkQÿmKͥF

    u

    160 140
    7

    

    x
    x
    x
    x
    x
    x

    7QKkQEҵQJYLӃW
    7QKkQEҵQJYLӃWQKӟ
    7QKkQEҵQJWKrPEҵQJYLӃW
    7QKkQEҵQJYLӃW
    7QKkQEҵQJYLӃWQKӟ
    7 nhân 1 EҵQJWKrPEҵQJYLӃW
    160 140 u 

    +2Ć7ûı1*

    1

    ĈһWWtQKUӗLWtQK
       u u  u

    4

    2

    Ĉ6 ?

    u

    
    
     ?

    3

    u

    
    

    u

    650 000 ?

    
    5

     ?

    %yQJ ÿqQ WURQJ QKj Fy WXәL WKӑ
    JLӡ%yQJÿqQÿѭӡQJFyWXәL
    WKӑJҩSOҫQWXәLWKӑFӫDEyQJÿqQ
    WURQJQKj+ӓLWXәLWKӑFӫDEyQJÿqQ
    ÿѭӡQJOjEDRQKLrXJLӡ"

    /8<ğ17ď3

    1

    ĈһWWtQKUӗLWtQK
      u u  u

    2

    &KӑQFkXWUҧOӡLÿ~QJ
    5{EӕWFyÿӗQJ5{EӕWPXDEӝFӡYXDPӛLEӝFyJLiÿӗQJ
    +ӓL5{EӕWFzQOҥLEDRQKLrXWLӅQ"
    $ÿӗQJ     %ÿӗQJ   

    3

    &ÿӗQJ

    7tQKJLiWUӏFӫDELӇXWKӭF
     D uE ±u 4

    4

    5{EӕW ÿһW FiF KҥW WKyF YjR EjQ Fӡ
    WKHR TX\ WҳF { WKӭ QKҩW ÿһW  KҥW
    WKyF{WKӭKDLÿһWKҥWWKyF{WKӭ
    EDÿһWKҥWWKyFYjFӭQKѭYұ\Vӕ
    WKyF ÿһW YjR { VDX JҩS ÿ{L Vӕ WKyF
    ÿһW YjR { WUѭӟF ÿy %LӃW UҵQJ { WKӭ
    PѭӡLWiPÿһWKҥWWKyF+ӓL
    5{EӕWÿһWEDRQKLrXKҥWWKyFYjR{
    WKӭKDLPѭѫL"
    5

    Bài 39

    &+,$&+26ž&0Ɔ7&+Ɯ6ž

    KKÀPSKÀ

    &΁NL͗QWKͻNKrQKÿ́ͻF
    PͱWK̹WJ̹RWKuW̽WF̻NL͗QWKͻ
    WURQJWͭNKrQKÿ́ͻF
    EDRQKLrXK̹WJ̹RQK͡"

    D

    7URQJWͭFK~QJWDFy
    NL͗QWKͻ

    7KΉFKL͟QẂ˿QJWΉ
    QḰSKpSFKLDÿmKͥF

    
     
    07
       
        
    0

     "

    x 1FKLDÿѭӧFYLӃW
      QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    5QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥFKLDÿѭӧFYLӃW
    1QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    4QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    6QKkQEҵQJWUӯEҵQJYLӃW
    5

     
    6

    E  "
    
     
    07
       
        
    4

    x 1FKLDÿѭӧFYLӃW
      QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    5QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥFKLDÿѭӧFYLӃW
    1QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    4QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    6QKkQEҵQJWUӯEҵQJYLӃW
    5

      Gѭ

    +2Ć7ûı1*

    1

    ĈһWWtQKUӗLWtQK
         

    2

    %ҥQ1DPWKӵFKLӋQKDLSKpSFKLDQKѭVDX
    
    40

    7
    457

    
    15

    

    

    

    

      Gѭ 

    6
    

     

    %ҥQ1DPWtQKÿ~QJKD\VDL"1ӃXVDLHPKm\VӱDOҥLFKRÿ~QJ

    3

    &{/DQFyÿӗQJ6DXNKLPXDNJ[RjLWKuF{FzQÿӗQJ
    +ӓLPӛLNLO{JDP[RjLJLiEDRQKLrXWLӅQ"
    7

    /8<ğ17ď3

    1

    ĈһWWtQKUӗLWtQK
         

    2

    7uPKDLVӕELӃWWәQJYjKLӋXFӫDFK~QJOҫQOѭӧWOjYj

    3

    &ӭKӝSVӳDÿyQJÿѭӧFWKjQKPӝWYӍVӳD+ӓLKӝSVӳDÿyQJ
    ÿѭӧFWKjQKQKLӅXQKҩWEDRQKLrXYӍVӳDYjFzQWKӯDPҩ\KӝSVӳD"

    4

    &KӑQFkXWUҧOӡLÿ~QJ
    $OLEDEDFyÿӗQJWLӅQYjQJ$OLEDEDFKLDVӕÿӗQJWLӅQYjQJ
    WKjQKSKҫQEҵQJQKDXUӗLOҩ\PӝWSKҫQFKLDFKRQKӳQJQJѭӡLGkQQJKqR
    +ӓL$OLEDEDFzQOҥLEDRQKLrXÿӗQJWLӅQYjQJ"
    $ 50 000

    5

    %& 150 000

    &KӑQFkXWUҧOӡLÿ~QJ
    .ӃWTXҧFӫDSKpSWtQKJKL
    WUrQ PӛL [H Oj WәQJ FkQ
    QһQJ WtQK WKHR ÿѫQ Yӏ
    NLO{JDP  FӫD [H Yj
    KjQJKRiWUrQFKLӃF[Hÿy
    +ӓL FKLӃF [H QjR Fy WKӇ
    ÿLTXDFk\FҫX"
    $
    %
    

    8

    1K·QJ[HFyFkQQ͏QJ WtQKF̻[HYj
    KjQJKRi OͳQK˿QW̽QV͕NK{QJ
    ÿ́ͻFÿLTXDFk\F̿XQj\

    &
    

    

    Bài 40

    7Š1+&+Œ7*,$2+2~1
    9}.Ŭ7+Ɛ3&Ɣ$3+†31+1

    KKÀPSKÀ
    D 
    &yFͱWPͯLFͱW
    FyP͏WF́͵LQrQ
    FyuP͏WF́͵L

    &yKjQJPͯLKjQJ
    FyP͏WF́͵LQrQFy
    uP͏WF́͵L

    &yEDRQKLrX
    P͏WF́͵LQK͡"
    &̻KDLE̹Q
    ÿ͙Xÿ~QJ

    × 4 = 4 ×
    E 7tQKJLiWUӏFӫDKDLELӇXWKӭFDuEYjEuD
    D

    b

    Du b

    b uD

    

    5

    u 5 = 15

    5 u 

    4

    6

    4 u 

    6 u 

    5

    

    5 u 

    u 5 = 40

    1KұQWKҩ\JLiWUӏFӫDDuEYjFӫDEuDOX{QEҵQJQKDXWDYLӃW
    Du b = b uD
    .KLÿәLFKӛFiFWKӯDVӕWURQJPӝWWtFKWKuWtFKNK{QJWKD\ÿәL
    9

    +2Ć7ûı1*

    1

    7uPFiFFһSSKpSWtQKFyFQJNӃWTXҧ

    u 510

    u 7
    51 u

    510 u

    7 u
    7 u

    u 7

    2

    u 51

    6ӕ ?
    D u u ?           E u 10 = ? u 5
    F u  ? u      G u u ?

    3

    7URQJE·DWL͟F
    FyEjQPͯL
    EjQFyÿͿQJ́͵L

    9ͅ\FyuQJ́͵L
    1ḰQJOjPVDRWtQK
    ÿ́ͻFN͗WTX̻QK͡"

    +m\V΅GͽQJWtQK
    FK̽WJLDRKRiQ
    FͿDSKpSQKkQ

    'QJWtQKFKҩWJLDRKRiQÿӇWuPNӃWTXҧFӫDSKpSWtQKu
    10

    KKÀPSKÀ
    D 
    .KͩLKͱSFK·QKͅW
    Qj\JͫPEDRQKLrX
    NKͩLOͅSSḰ˿QJQKͧ"

    .KͩLQj\
    JͫP u uNKͩL
    OͅSSḰ˿QJQKͧ

    .KͩLQj\JͫP
    u uKD\u u 
    NKͩLOͅSSḰ˿QJQKͧ
    &̻KDLE̹Q
    ÿ͙Xÿ~QJ

    × × × ×
    E 7tQKJLiWUӏFӫDKDLELӇXWKӭF DuE uFYjDu EuF 
    D

    b

    F

    DuE uF

    Du EuF

    5

    4

    

    u u 

    5 u u  

    6

    

    

    u u 

    6 u u  

    

    

    5

    u u 

    u u  

    1KұQWKҩ\JLiWUӏFӫD DuE uFYjFӫDDu EuF OX{QEҵQJQKDXWDYLӃW
    DuE uF Du EuF
    .KLQKkQPӝWWtFKKDLVӕYӟLVӕWKӭEDWDFyWKӇQKkQVӕWKӭQKҩW
    YӟLWtFKFӫDVӕWKӭKDLYjVӕWKӭED

    11

    +2Ć7ûı1*

    1

    7tQKEҵQJKDLFiFK WKHRPүX 
    0үXuu "
      &iFKuu  u u u 
      &iFKuu u u  u 
    4 uu 5

    2

    7 uu

    6 uu

    6 uu 4

    &iFEҥQFKLDWKjQKKDLÿӝLÿӇFKѫLWUzFKѫL+m\[iFÿӏQKWKjQKYLrQFӫD
    PӛLÿӝLELӃWUҵQJFiFWKjQKYLrQWURQJFQJPӝWÿӝLFҫPPLӃQJEuDJKL
    ELӇXWKӭFFyJLiWUӏEҵQJQKDX
    u 5 u
    u

    6

    u

    
    uu

    40 u
    u

    3

    12

    5{EӕW OjP  FKLӃF EiQK NHP
    0ӛL FKLӃF EiQK NHP ÿѭӧF FҳW
    WKjQK  SKҫQ PӛL SKҫQ Fy 
    TXҧGkXWk\+ӓL5{EӕWÿmGQJ
    WҩWFҧEDRQKLrXTXҧGkXWk\"

    10

    /8<ğ17ď3

    1

    2

    6ӕ ?
    D

    b

    F

    Du b

    b uD

    DuE uF

    Du EuF

    7

    5

    

    ?

    ?

    ?

    ?

    

    

    

    ?

    ?

    ?

    ?

    10

    

    4

    ?

    ?

    ?

    ?

    %LӃWu Yju 
    .K{QJWKӵFKLӋQSKpSWtQKHPKm\FKRELӃWJLiWUӏFӫDPӛLELӇXWKӭFVDX
     u  u
     uu 5

    3

    5 uu

    *LҧL{FKӳGѭӟLÿk\
    L

    400
    ?

    Q

    
    ?

    
    ?

    Ĉ

    600
    ?

    1

    %LӃWUҵQJ
    Ê 4 uu 5
    Ý 4 uu
    Ô 6 u 50 u
    8 uu 4

    4

    6ӕ ?
    D u 7 = 7 u ?
    E u  ?  u
    F  u u u ? u
    G uu 4 = 4 u ?  u ?
    13

    Bài 41

    1+1&+,$9ƈ,ƺ

    KKÀPSKÀ

    &yW̽WF̻EDR
    QKLrXOiF͵QK͡"

    u

    &yGk\F͵
    PͯLGk\Fy
    OiF͵
    7ͳFyWK͛QḰP
    QJD\ÿ́ͻF
    N͗WTX̻ÿ̽\

    D

    u 10 = ?
    u 10 = 10 u1KҭPFKөFu FKөF 
    9ұ\u 
    1JѭӧFOҥLWӯu 
       WDFy 

    E

    u 100 = ?
    u u u   u u u 
    1JѭӧFOҥL 
    7ѭѫQJWӵWDFy
    u 
     

    1KұQ[pW
    x .KLQKkQPӝWVӕWӵQKLrQYӟL«WDYLӃWWKrPPӝWKDL
    ED«FKӳVӕYjRErQSKҧLVӕÿy
    x .KLFKLDVӕWUzQFKөFWUzQWUăPWUzQQJKuQ«FKR«
    WDEӓEӟWÿLPӝWKDLEDFKӳVӕӣErQSKҧLVӕÿy
    14

    +2Ć7ûı1*

    1

    7tQKQKҭP
    14 uuu 1 000
     

    2

    5{EӕWFKҥ\YzQJTXDQKVkQYұQÿӝQJ%LӃWPӛLYzQJTXDQKVkQGjL
    P+ӓL5{EӕWÿmFKҥ\EDRQKLrXPpW"

    3

    4XDQViWWUDQKUӗLWUҧOӡLFkXKӓL

    &yKjQJJK͗

    7URQJ KӝL WUѭӡQJ FiF KjQJ JKӃ ÿѭӧF [ӃS ÿӅX QKDX ӣ KDL ErQ OӕL ÿL
    %LӃWPӛLKjQJJKӃӣKDLErQOӕLÿLÿӅXFyFKӛQJӗL+ӓLKӝLWUѭӡQJFy
    WҩWFҧEDRQKLrXFKӛQJӗL"

    15

    /8<ğ17ď3

    1

    2

    3

    6ӕ ?
    6ӕEӏFKLD

    

    4 500

    57 000

    

    ?

    ?

    6ӕFKLD

    10

    100

    ?

    ?

    

    

    7KѭѫQJ

    ?

    ?

    1 000

    10

    1 000

    100

    6ӕ ?
    D NJ  ? Wҥ   

       E
     NJ  ? \ӃQ

    \ӃQ  ? Wҥ  

        NJ  ? Wҥ

    NJ  ? WҩQ  

        NJ  ? WҩQ

    7tQKEҵQJFiFKWKXұQWLӋQ
    D   u
       5 u
            E   uu
    F   uu
        5       G

    5 uu

    4

    0ӝWÿRjQWjXKRҧFyWRD1JѭӡLWDVӱGөQJFiFWRDWjXWӯWRDÿӃQ
    WRDÿӇFKӣKjQJ%LӃWPӛLWRDFKӣWҩQKjQJ+ӓLÿRjQWjXFKӣWҩWFҧ
    EDRQKLrXWҩQKjQJ"

    5

    7UrQÿRҥQÿѭӡQJGjLPFӭPFyPӝWFӝWÿqQ%LӃWFҧKDLÿҫXÿRҥQ
    ÿѭӡQJÿӅXFyFӝWÿqQ+ӓLWUrQÿRҥQÿѭӡQJÿyFyEDRQKLrXFӝWÿqQ"

    16

    Bài 42

    7Š1+&+Œ73+13+ž,&Ɣ$
    3+†31+1Ëž,9ƈ,3+†3&Ɔ1*

    KKÀPSKÀ
    0ӝWÿӝLÿӗQJGLӉQFyKjQJPһFiRÿӓYjKjQJPһFiRYjQJPӛLKjQJ
    ÿӅXFyQJѭӡL+ӓLÿӝLÿӗQJGLӉQÿyFyWҩWFҧEDRQKLrXQJѭӡL"
    7ͳWtQKULrQJVͩQJ́͵LP͏FiRÿͧ
    VͩQJ́͵LP͏FiRYjQJUͫLFͱQJO̹L

    7ͳWtQKWͭQJVͩKjQJWÚͳFUͫL
    WtQKVͩQJ́͵LͷFiFKjQJÿy

    15 u   u 5

    15 uu 

        

         

     QJѭӡL 

     QJѭӡL 

    15 u   uu
    x .KL QKkQ PӝW Vӕ YӟL PӝW WәQJ WD Fy WKӇ QKkQ
    VӕÿyYӟLWӯQJVӕKҥQJFӫDWәQJUӗLFӝQJFiF
    NӃWTXҧYӟLQKDX
    Du EF  D×EDuF
    x .KLQKkQPӝWWәQJYӟLPӝWVӕWDFyWKӇQKkQ
    WӯQJVӕKҥQJFӫDWәQJYӟLVӕÿyUӗLFӝQJFiF
    NӃWTXҧYӟLQKDX
    DE uF DuFEuF

    Ĉk\OjWtQKFK̽W
    SKkQSKͩLFͿD
    SKpSQKkQÿͩL
    YͳLSKpSFͱQJ

    +2Ć7ûı1*

    1

    7tQKEҵQJKDLFiFK WKHRPүX 
    0үXu 
    &iFK
    u   u
         

    &iFK
    u   uu 4
         
         

    D u         E   u 7
    17

    2

    D 7tQKJLiWUӏFӫDFiFELӇXWKӭFVDXYӟLP Q S 
    PQ uS

    P× QS

    PuQPuS

    PuSQuS

    E +DLELӇXWKӭFQjRӣFkXDFyJLiWUӏEҵQJQKDX"

    3

    .KӕLOӟS%ӕQFyOӟSKӑFYӁNKӕLOӟS%DFyOӟSKӑFYӁPӛLOӟSKӑFYӁ
    FyEҥQ+ӓLFҧKDLNKӕLOӟSFyEDRQKLrXEҥQKӑFYӁ"

    /8<ğ17ď3

    1

    7tQKEҵQJKDLFiFK WKHRPүX 

    7tQKE͉QJFiFK
    WKXͅQWL͟QK˿Q

    0үXuu
    &iFK

    &iFK

    uu 

    uu u 

         

         

    u 10

         

    

    

    D uu 5
    E uu

    2

    7tQKEҵQJFiFKWKXұQWLӋQ
    D uu 7
    E uu 4
    F uu 6

    3

    7tQK WKHRPүX 
    0үXuuu
    uuu u 
               u
               
    uuu

    18

    4

    1JѭӡLWDFKX\ӇQKjQJÿӇJL~SÿӥÿӗQJEjRYQJONJOөWĈӧWPӝWFKX\ӇQ
    ÿѭӧF  FKX\ӃQ PӛL FKX\ӃQ Fy  WKQJ KjQJ ĈӧW KDL FKX\ӇQ ÿѭӧF
    FKX\ӃQPӛLFKX\ӃQFyWKQJKjQJ+ӓLFҧKDLÿӧWÿmFKX\ӇQÿѭӧF
    EDRQKLrXWKQJKjQJ"

    /8<ğ17ď3

    1

    7tQKUӗLVRViQKJLiWUӏFӫDKDLELӇXWKӭF WKHRPүX 
    0үX4 u ± Yju±u
    4 u ±  u 4

    4 u±u ±

       

          

    

    7DFyu ±  u±u
    D u ± Yju±u 4
    E  ± uYju±u

    2

    D 7tQKJLiWUӏFӫDELӇXWKӭF WKHRPүX 
    D

    b

    F

    Du E±F

    DuE±DuF

    5

    

    

    5 u ±  

    5 u±u 

    

    7

    

    ?

    ?

    14

    10

    5

    ?

    ?

    E >; <; = ?
    Du E±F  ? DuE±DuF

    3

    7tQKEҵQJFiFKWKXұQWLӋQ
    D u±u        E u±u

    4

    0ӝWFӱDKjQJFyWҩPYҧLKRDPӛLWҩPGjLP&ӱDKjQJÿmEiQ
    ÿѭӧF  WҩP YҧL KRD QKѭ Yұ\ +ӓL FӱD KjQJ FzQ OҥL EDR QKLrX PpW
    YҧLKRD"

    19

    Bài 43

    1+19ƈ,6ž&+$,&+Ɯ6ž
    0ͯL{W{FKͷKͥFVLQK{W{
    QḰWK͗FKͷEDRQKLrXKͥFVLQK"

    KKÀPSKÀ

    u "
    7DFyWK͛WtQKQḰVDX

      u
        
        
    

    7K{QJWḰ͵QJWDÿ͏W
    WtQKUͫLWtQKQḰVDX

    u

    
    1
    

    
    

    u 
    uu
    
    

    x QKkQEҵQJYLӃWQKkQ
    EҵQJYLӃW
     QKkQEҵQJYLӃW GѭӟL 
    QKkQEҵQJYLӃW
    x +ҥ   FӝQJ  EҵQJ  YLӃW 
    QKӟWKrPEҵQJYLӃW

    /ѭXê
    x OjWtFKULrQJWKӭQKҩW ÿѫQYӏ 
    x 4OjWtFKULrQJWKӭKDL FKөFKD\ÿѫQYӏ 
    x VLӃWWtFKULrQJWKӭKDLOLVDQJWUiLPӝWFӝW VRYӟLWtFKULrQJWKӭQKҩW 
    20

    +2Ć7ûı1*

    1

    ĈһWWtQKUӗLWtQK
    uuu

    2

    &KӑQNӃWTXҧWKtFKKӧSFKRPӛLSKpSWtQK
    u16

    45 u

    

    3

    u14

    504

    

    &ӱDKjQJFyEDRQJ{PӛLEDRFkQQһQJNJ+ӓLFӱDKjQJÿyFy
    WҩWFҧEDRQKLrXNLO{JDPQJ{"

    /8<ğ17ď3

    1

    2

    6ӕ ?
    7KӯDVӕ

    

    

    

    66

    7KӯDVӕ

    

    

    

    

    7tFK

    

    ?

    ?

    ?

    7tQK
    D u    u   u

    u 50

    0үXu  u u 
    E u   u   u 50

    17 000 u

    0үXu  u u 

    3

    7tQKGLӋQWtFK6FӫDKuQKFKӳQKұWFyFKLӅXGjLD
    YjFKLӅXUӝQJEWKHRF{QJWKӭF
    D
    6 DuE DEFQJÿѫQYӏÿR 
    D 9ӟLD FPE FP
    E 9ӟLD PE P

    6 "

    b

    21

    4

    0ӝW FӱD KjQJ KRD TXҧ EiQ ÿѭӧF
    NJ[RjLYjNJFDP%LӃWNJ
    [RjLJLiÿӗQJNJFDPJLi
    ÿӗQJ+ӓLFӱDKjQJÿyEiQ
    [RjLYjFDPÿѭӧFEDRQKLrXWLӅQ"

    /8<ğ17ď3

    1

    D ĈһWWtQKUӗLWtQK
       u      u     u
    E 6ӕ ?

    2

    u 11

    

    ±

    ?

    

    ?

    7ӯFiFWKӯDVӕYjWtFKWѭѫQJӭQJKm\OұSFiFSKpSQKkQWKtFKKӧS
    7KӯDVӕ
    

    7KӯDVӕ
    

    

    7tFK

    60

    576

    

    3

    +ӝS$ÿӵQJJyLNҽRFKDQKPӛLJyLFyFiLNҽR+ӝS%ÿӵQJJyL
    NҽR GӯD PӛL JyL Fy  FiL NҽR +ӓL Vӕ NҽR ӣ KDL KӝS KѫQ NpP QKDX
    EDRQKLrXFiL"

    4

    D  ? ?
    u

    
    11
    

    u

    
    11
    

    

    

     ?

    54

    ?

    E .KLQKkQPӝWVӕYӟL1DPÿmÿһWKDLWtFKULrQJWKҷQJFӝWQrQNӃWTXҧ
    Oj+ӓLVӕÿyOjVӕQjR"
    22

    Bài 44

    &+,$&+26ž&+$,&+Ɯ6ž

    KKÀPSKÀ
    M DÖ\ ‡Õa " WTuOT Pa XžOT X„Z  `TaeÕZ 4 U Y£U `TaeÕZ O} NM[ ZTU„a
    WTuOT Pa XžOT+

     "
    7DFyWKӇÿһWWtQKUӗLWtQKQKѭVDX
    

    

    

    

    
    
    0

    x
    
    
    
    x
    
    
    

    FKLDÿѭӧFYLӃW
    QKkQEҵQJYLӃW
    QKkQEҵQJYLӃW
    WUӯEҵQJYLӃW
    +ҥÿѭӧFFKLDÿѭӧFYLӃW
    QKkQEҵQJYLӃWQKӟ
    QKkQEҵQJWKrPEҵQJYLӃW
    WUӯEҵQJYLӃW
     

    23

    E  ;ӃS  iR SKDR OrQ FiF WKX\ӅQ PӛL WKX\ӅQ  iR SKDR +ӓL [ӃS
    ÿѭӧFQKLӅXQKҩWEDRQKLrXWKX\ӅQYjFzQWKӯDPҩ\iRSKDR"
     "
    7DFyWKӇÿһWWtQKUӗLWtQKQKѭVDX
    

    

    

    

    
    
    

    x FKLDÿѭӧFYLӃW
    1QKkQEҵQJYLӃW
    1QKkQEҵQJYLӃW
     WUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
     QKkQEҵQJYLӃWQKӟ
     QKkQEҵQJWKrPEҵQJYLӃW
     WUӯEҵQJYLӃW
      Gѭ

    +2Ć7ûı1*

    1

    ĈһWWtQKUӗLWtQK
               
               

    2

    7tQK
    D           
    0үX "
    &QJ[RiFKӳVӕӣWұQFQJVӕFKLDYjVӕEӏFKLDUӗLWKӵFKLӋQ
    SKpSFKLD
    9ұ\  

    24

    E       
    0үX "
    &QJ[RiFKӳVӕӣFXӕLFӫDVӕFKLDYjVӕEӏFKLDUӗLWKӵFKLӋQ
    SKpSFKLD
    9ұ\  

    3

    7URQJPӝWKӝLWUѭӡQJQJѭӡLWD[ӃSFiLJKӃYjRFiFGm\PӛLGm\
    JKӃ+ӓL[ӃSÿѭӧFEDRQKLrXGm\JKӃQKѭYұ\"

    /8<ğ17ď3

    1

    ĈһWWtQKUӗLWtQK WKHRPүX 
    D           
    0үX

    

    

    

    

    00

    x FKLDÿѭӧFYLӃW
    QKkQEҵQJWUӯEҵQJYLӃW
    QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    QKkQEҵQJWUӯEҵQJYLӃW
    QKӟ
    QKkQEҵQJWKrPEҵQJWUӯ
    EҵQJYLӃW

    E           
    0үX

    
    
    00

    xFKLDÿѭӧFYLӃW
     QKkQEҵQJWUӯEҵQJYLӃW
    QKkQEҵQJWUӯEҵQJYLӃW
    x +ҥFKLDÿѭӧFYLӃW
    x +ҥÿѭӧFFKLDÿѭӧFYLӃW
    QKkQEҵQJWUӯEҵQJYLӃW
    QKӟ
     QKkQ  EҵQJ  WKrP  EҵQJ   WUӯ 
    EҵQJYLӃW
    

    25

    2

    7tQKJLiWUӏUӗLVRViQKJLiWUӏFӫDFiFELӇXWKӭFVDX
    D   u            
    E  u      u    u 

    3

    0ӝWVkQEyQJÿiKuQKFKӳQKұWFyGLӋQWtFKPFKLӅXUӝQJP
    7tQKFKXYLFӫDVkQEyQJÿiÿy

    /8<ğ17ď3

    1

    2

    3

    6ӕ ?
    7KӯDVӕ

    

    

    

    ?

    7KӯDVӕ

    45

    

    ?

    56

    7tFK

    

    ?

    

    7 000

    6ӕ ?
    6ӕEӏFKLD

    6ӕFKLD

    7KѭѫQJ

    6ӕGѭ

    9LӃWOj

    

    45

    

    5

      Gѭ

    

    

    ?

    ?

     " Gѭ"

    &KӑQFkXWUҧOӡLÿ~QJ
    0ӝWÿӝLÿӗQJGLӉQ[ӃSWKjQKKjQJPӛLKjQJFyQJѭӡL1ӃXÿӝL
    ÿӗQJ GLӉQ ÿy [ӃS PӛL KjQJ  QJѭӡL WKu [ӃS ÿѭӧF EDR QKLrX KjQJ
    QKѭYұ\"
    $ 15

    4

    26

    %     &    '

    0ӛLEiQK[HÿҥSFҫQFyQDQKRD+ӓLFyQDQKRDWKuOҳSÿѭӧF
    QKLӅXQKҩWFKREDRQKLrXFKLӃF[HÿҥSKDLEiQKYjFzQWKӯDEDRQKLrX
    QDQKRD"

    Bài 45

    7+ƞ&+}1+9}75Ő,1*+,Ŵ0
    ĭƈ&/ĭƐ1*7521*7Š1+72~1

    +2Ć7ûı1*

    &̻QJj\K{PTXDFyNKR̻QJP̽\QJKuQ
    ÓͻWNKiFKWKDPTXDQF{QJYLrQQK͡"

    7URQJ PӝW QJj\ &Kӫ QKұW 5{EӕW
    FQJFiFEҥQWKDPTXDQF{QJYLrQ

    1

    9ӯDÿӃQFәQJKѭӟQJGүQYLrQFKR
    ELӃWWURQJQJj\K{PTXDEXәLViQJ
    YjEXәLFKLӅXOҫQOѭӧWFyYj
    OѭӧWNKiFKWKDPTXDQ
    5{EӕWѭӟFOѭӧQJQKѭVDX
    /jPWUzQWKjQKOjPWUzQWKjQK9ұ\FҧQJj\
    K{PTXDFyNKRҧQJOѭӧWNKiFKWKDPTXDQF{QJYLrQ
    (PKm\ѭӟFOѭӧQJNӃWTXҧPӛLSKpSWtQKWKHRPӛL\rXFҫXVDX
    .KRҧQJPҩ\QJKuQ"
    
    ±

    2

    .KRҧQJPҩ\FKөFQJKuQ"
    
    ±

    6DXÿy5{EӕWYjFiFEҥQÿӃQYѭӡQWKҧRPӝF

    'L͟QWtFKP̻QKÝ͵Q$
    OͳQK˿QP2

    P
    P
    A

    &KL͙XUͱQJ
    P̻QKÝ͵Q%
    EpK˿QP

    P

    x1DPVDLUͫL/jPWUzQ

    OrQWKjQKOjPWUzQ
    OrQWKjQK'L͟QWtFK
    P̻QKÝ͵Q$NK{QJWK͛
    OͳQK˿Qu  P2 
    x0DLFNJQJVDL/jPWUzQ
    [XͩQJWKjQK
    &KL͙XUͱQJP̻QKÝ͵Q
    %NK{QJWK͛EpK˿Q
      P 

    P
    B

    'ӵDYjRFiFKѭӟFOѭӧQJFӫD5{EӕWHPKm\FKRELӃWFiFNKҷQJÿӏQKVDX
    ÿ~QJKD\VDL
    D u!    E 
    27

    3

    ĈӃQPӝWNKXÿҩWUӝQJ5{EӕWWәFKӭFPӝWWUzFKѫL(PYjFiFEҥQFQJ
    WKDPJLDWUzFKѫLQj\QKp

    75´Ď+ā,
    z Å Î- & z4

    &KXҭQEӏ
    x KҿÿѭӡQJÿXDQKѭKuQKYӁ
    x CiFWҩPEuDJKLVҹQFiFSKpSWtQK u 
    7±   u 
    ± u   
    x FӡKLӋXPjX[DQKFӡKLӋXPjXÿӓ
    CiFKFKѫL
    x +DLÿӝLFKѫLPӛLÿӝLFӱPӝWQJѭӡLÿyQJYDLQJӵDÿXDYjÿӭQJӣ{
    [XҩWSKiWWUrQÿѭӡQJÿXDFӫDÿӝLPuQK
    x MӛLOѭӧWFKѫLWUӑQJWjLJLѫPӝWSKpSWtQKUӗLK{NKҭXOӋQK³Ĉ~QJKD\
    VDL"´1ӃXNӃWTXҧSKpSWtQKÿyOjÿ~QJWKuÿӝLWUѭӣQJFӫDPӛLÿӝLJLѫ
    FӡKLӋXPjX[DQKQӃXVDLWKuJLѫFӡKLӋXPjXÿӓ
    x TUӑQJWjL[iFÿӏQKÿӝLJLѫFӡKLӋXFKtQK[iF
    WKuFK~QJӵDÿXDFӫDÿӝLÿyWLӃQPӝW{WUrQ
    ÿѭӡQJ ÿXD QJѭӧF OҥL WKu ÿӭQJ \rQ &K~
    QJӵDÿXDFӫDÿӝLQjRYӅÿӃQ{ÿtFKWUѭӟFWKu
    ÿӝLÿyJLjQKFKLӃQWKҳQJ

    28

    Bài 46

    7‰06ž7581*%‰1+&Ɔ1*

    KKÀPSKÀ
    D

    7UXQJEuQKPͯL
    QJj\0DLWͅS
    WK͛GͽFSK~W

    +{PTXDWͳWͅS
    WK͛GͽFSK~W
    +{PQD\WͳWͅS
    SK~Wÿ͛E
    FKRK{PTXD

    &KiXQrQWͅSWK͛GͽF
    ÿ͙Xÿ͏QPͯLQJj\
    SK~WV͕WͩWK˿Q
    FKRV΁FNKR͓

    7DWKҩ\   
    7DJӑLOjVӕWUXQJEuQKFӝQJFӫDKDLVӕYj
    E &iFKWuPVӕWUXQJEuQKFӝQJ
    9tGө7uPVӕWUXQJEuQKFӝQJFӫDEDVӕYj
    /ҩ\WәQJFӫDEDVӕYjFKLDFKRWDÿѭӧF
      
    7DJӑLOjVӕWUXQJEuQKFӝQJFӫDEDVӕYj
    0XӕQWuPVӕWUXQJEuQKFӝQJFӫDQKLӅXVӕWDWtQKWәQJ
    FӫDFiFVӕÿyUӗLFKLDWәQJÿyFKRVӕFiFVӕKҥQJ

    +2Ć7ûı1*

    1

    7uPVӕWUXQJEuQKFӝQJFӫDFiFVӕVDX
    D YjE Yj    F Yj

    2

    D 6ӕFk\WUӗQJÿѭӧFFӫD
    ÿӝLOҫQOѭӧWOjFk\
     Fk\ Yj  Fk\ +ӓL
    WUXQJEuQKPӛLÿӝLWUӗQJ
    ÿѭӧFEDRQKLrXFk\"

    %jLJL̻L
    7UXQJEuQKPӛLÿӝLWUӗQJÿѭӧFVӕFk\Oj
       Fk\
    ĈiSVͩFk\

    E 6ӕKӑFVLQKFӫDOӟSOҫQOѭӧWOjYj+ӓLWUXQJEuQKPӛL
    OӟSFyEDRQKLrXKӑFVLQK"
    29

    3

    7URQJPӝWJLҧLÿXD[HÿҥS[X\rQ9LӋWOӝWUuQKPӝWVӕFKһQJÿXDÿѭӧF
    FKRQKѭEҧQJGѭӟLÿk\
    &KһQJ

    ĈRҥQÿѭӡQJ

    ĈӝGjL NP

    1

    9zQJTXDQKWKjQKSKӕ/ҥQJ6ѫQ

    60

    

    /ҥQJ6ѫQWӟL+j1ӝL

    160

    

    YzQJTXDQKKӗ+RjQ.LӃP

    

    4

    +j1ӝLWӟL7KDQK+Ri

    154

    +ӓLWUXQJEuQKPӛLFKһQJGjLEDRQKLrXNLO{PpW"

    /8<ğ17ď3

    1

    7uP Vӕ JKL ӣ PӛL QKXӷ KRD ELӃW
    VӕJKLӣQKө\KRDEҵQJWUXQJEuQK
    FӝQJFӫDFiFVӕJKLӣFiQKKRD

    17

    
    

    15

    ?
    

    

    ?

    
    

    2

    1KjEiF9kQFyEDRWKyFWҿFkQQһQJNJYjEDRWKyFQӃSFkQ
    QһQJ  NJ +ӓL WUXQJ EuQK PӛL EDR WKyF QKj EiF 9kQ FkQ QһQJ EDR
    QKLrXNLO{JDP"

    3

    1Jj\WKӭQKҩW5{EӕWOjPÿѭӧFFiLEiQKJLҫ\1Jj\WKӭKDL5{EӕW
    OjPÿѭӧFQKLӅXKѫQQJj\WKӭQKҩWFiLEiQK+ӓLWUXQJEuQKPӛLQJj\
    5{EӕWOjPÿѭӧFEDRQKLrXFiLEiQKJLҫ\"

    4

    4XDQViWWUDQKUӗLWUҧOӡLFkXKӓL
    5{EͩWYL͗W
    VͩJuYͅ\"

    5{EӕWÿmYLӃWVӕQjR"
    30

    Ĉͩ1DPÿ̽\7ͳJͻL
    êOjWUXQJEuQKFͱQJ
    FͿDKDLVͩGRWͳYj
    0DLYL͗WE͉QJ

    Bài 47

    %},72~1/,‡148$1ËŬ1
    5—79ŮËī19Ÿ

    KKÀPSKÀ

    KͱSEiQKQḰYͅ\
    FyEDRQKLrXFiL
    EiQKQK͡"

    &yFiLEiQK[͗S
    ÿ͙XYjRKͱS

    7ÚͳFWLrQWuPVͩEiQK
    WURQJKͱSUͫLWuPVͩEiQK
    WURQJKͱSQKp

    FiLEiQK

    ? FiLEiQK
    7yPW͇W
    KӝSFiLEiQK
    KӝS«FiLEiQK"

    %jLJL̻L
    6ӕEiQKWURQJPӛLKӝSOj
      FiL
    6ӕEiQKWURQJKӝSOj
    6 u  FiL
    ĈiSVͩFiLEiQK

    +2Ć7ûı1*

    1

    &y  NJ ÿѭӡQJ FKLD ÿӅX YjR  W~L +ӓL  W~L QKѭ Yұ\ Fy EDR QKLrX
    NLO{JDPÿѭӡQJ"

    2

    ;ӃSÿӅXTXҧWUӭQJYjRNKD\+ӓLNKD\WUӭQJQKѭYұ\FyEDRQKLrX
    TXҧ"

    3

    6ӕ ?
    6ӕNLO{JDPPXӕL

    

    6ӕWLӅQWѭѫQJӭQJ ÿӗQJ 11 000

    1

    4

    ?

    ?
    31

    KKÀPSKÀ
    &ylPͅWRQJ
    ÿΉQJÿ͙XYjRFDQ

    7yPW͇W
    lFDQ
    l«FDQ"

    1͗XFylPͅWRQJ
    WKuÿΉQJÿ͙XYjRÿ́ͻF
    P̽\FDQQḰYͅ\"

    7ÚͳFWLrQWuPVͩOtW
    PͅWRQJWURQJFDQ
    UͫLWuPVͩFDQÿ͛ÿΉQJ
    lPͅWRQJQKp

    %jLJL̻L
    6ӕOtWPұWRQJӣPӛLFDQOj
      l
    lPұWRQJÿӵQJÿӅXYjRVӕFDQOj
      FDQ
    ĈiSVͩFDQ

    +2Ć7ûı1*

    1

    9LӋWPXDFKLӃFWKѭӟFÿRJyFFQJORҥLSKҧLWUҧÿӗQJ+ӓL0DLFy
    ÿӗQJWKuPXDÿѭӧFPҩ\FKLӃFWKѭӟFÿRJyFORҥLÿy"

    2

    KӝSVӳDFKXDÿyQJÿӅXÿѭӧFYjRYӍ+ӓLKӝSVӳDFKXDFQJORҥL
    VӁÿyQJÿѭӧFPҩ\YӍQKѭYұ\"

    /8<ğ17ď3

    1

    7URQJSKRQJWUjR³ĈәLJLҩ\Oҩ\Fk\[DQK´9LӋWÿmÿәLNJJLҩ\ÿӇÿѭӧF
    Fk\+ӓL0DLÿәLNJJLҩ\FQJORҥLÿyWKuÿѭӧFPҩ\Fk\QKѭYұ\"

    2

    %ҥQ9LӋW[ӃSTXHWtQKÿӇÿѭӧFPӝWKuQKYX{QJFyFKXYLFP'QJ
    FiFTXHWtQKORҥLÿyEҥQ0DL[ӃSÿѭӧFFiFKuQKGѭӟLÿk\ NKRҧQJFiFK
    JLӳDFiFTXHWtQKOjNK{QJÿiQJNӇ +ӓLFKXYLPӛLKuQKÿyOjEDRQKLrX
    [ăQJWLPpW"

    32

    Bài 48

    /8<Ŵ17Ś3&+81*

    /8<ğ17ď3

    1

    2

    7tQKQKҭP
    D u      u

    u 1 000

    E  

    

    ĈһWWtQKUӗLWtQK
     u     

    3

     u

    

     ? ?
    7UѭӡQJ 7LӇX KӑF +Rj %uQK Fy KDL PҧQK YѭӡQ WUӗQJ KRD 0ҧQK YѭӡQ
    WUӗQJKRDKӗQJGҥQJKuQKFKӳQKұWFyFKLӅXGjLPFKLӅXUӝQJP
    0ҧQKYѭӡQWUӗQJKRDF~FGҥQJKuQKYX{QJFyFҥQKP

    D &KXYLFӫDKDLPҧQKYѭӡQEҵQJQKDX
    E 'LӋQ WtFK PҧQK YѭӡQ WUӗQJ KRD KӗQJ EҵQJ GLӋQ WtFK
    PҧQKYѭӡQWUӗQJKRDF~F
    F  'LӋQ WtFK PҧQK YѭӡQ WUӗQJ KRD KӗQJ Ep KѫQ GLӋQ WtFK
    PҧQKYѭӡQWUӗQJKRDF~F

    4

    ?
    ?
    ?

    .KӕLFӫD7UѭӡQJ7LӇXKӑF1JX\ӉQ7UmLJӗPOӟSFyKӑFVLQKYj
    OӟSPӛLOӟSFyKӑFVLQK+ӓLWUXQJEuQKPӛLOӟSNKӕLFӫDWUѭӡQJ
    WLӇXKӑFÿyF
     
    Gửi ý kiến