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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: 1.(x+y+z)^2 ; (x-y+z)^2 2.(x-y-z)^2 3.(a^2+2a+3)( a^2+2a-3) 4.(a^2+2a+3)( a^2-2a-3)

Tháng Mười Hai 30, 2022 Toán học 1 Comment 0 views

Toán Lớp 8: 1.(x+y+z)^2 ; (x-y+z)^2
2.(x-y-z)^2
3.(a^2+2a+3)( a^2+2a-3)
4.(a^2+2a+3)( a^2-2a-3)

Comments ( 1 )

  1. ankim
    ankim
    30 Tháng Mười Hai, 2022 at 10:57 chiều
    Reply
    Hướng dẫn giải:
    1.1, (x+y+z)^2
    =x^2+y^2+z^2+2xy+2xz+2yz
    1.2, (x-y+z)^2
    =x^2+(-y)^2+z^2+2x.(-y)+2xz+2.(-y)z
    =x^2+y^2+z^2+2x.(-y)+2xz+2.(-y)z
    =x^2+y^2+z^2-2xy+2xz+2.(-y)z
    =x^2+y^2+z^2-2xy+2xz-2yz
    2, (x-y-z)^2
    =x^2+(-y)^2+(-z)^2+2x(-y)+2x(-z)+2(-y)(-z)
    =x^2+y^2+z^2+2x(-y)+2x(-z)+2(-y)(-z)
    =x^2+y^2+z^2-2xy+2x(-z)+2(-y)(-z)
    =x^2+y^2+z^2-2xy-2xz+2(-y)(-z)
    =x^2+y^2+z^2-2xy-2xz+2yz
    3, (a^2+2a+3)(a^2+2a-3)
    =(a^2+2a)^2-9
    =a^4+4a^3+4a^2-9
    4, (a^2+2a+3)(a^2-2a-3)
    =a^4-(2a+3)^2
    =a^4-(4a^2+12a+9)
    =a^4-4a^2-12a-9
    _______________________________
    Công thức:
    @ (a+b+c)^2=a^2+b^2+c^2+2ab+2ac+2bc
    @ (-).(-)=(+)
    @ (a-b)(a+b)=a^2-b^2
    @ (a+b)^2=a^2+2ab+b^2

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222-9+11+12:2*14+14 = ? ( )

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