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

Toán Lớp 8: Câu 2: (x – y)2 bằng: A. x2 + y2 B. (y – x)2 C. y2 – x2 D. x2 – y2

Toán Lớp 8: Câu 2: (x – y)2 bằng:
A. x2 + y2
B. (y – x)2
C. y2 – x2
D. x2 – y2

Comments ( 2 )

  1. (x – y)^2
    = (y – x)^2
    => B
    GT:
    (A – B)^2 = (B – A)^2
     

  2. Câu 2:
    (x-y)^2
    = (x-y)(x-y)
    = x(x-y) – y(x-y)
    = x^2 – xy – xy + y^2
    = x^2 – 2xy + y^2
    = y^2 – 2xy + x^2
    = y^2 – 2.x.y + x^2
    = (y-x)^2
    => B. (y-x)^2

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

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