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

Toán Lớp 8: A = 2.(x-y)(x^2 +xy +y^2) – 3(x^2 + 2xy + y^2) = 4 (x2 + xy + y2) – 3×2 – 6xy – 3y2 = 4x^2 + 4xy + 4y^2 – 3x^

Toán Lớp 8: A = 2.(x-y)(x^2 +xy +y^2) – 3(x^2 + 2xy + y^2)
= 4 (x2 + xy + y2) – 3×2 – 6xy – 3y2
= 4x^2 + 4xy + 4y^2 – 3x^2 – 6xy – 3y^2
= x^2 – 2xy + y^2
Cho hỏi tại sao2.(x-y)(x^2 +xy +y^2) – 3(x^2 + 2xy + y^2)
= 4 (x2 + xy + y2) – 3×2 – 6xy – 3y2

Comments ( 1 )

  1. Đề bài phải cho: $x-y=2$ thì $2(x-y)(x^2 +xy +y^2) – 3(x^2 + 2xy + y^2)$
    $= 2.2(x^2+xy+y^2)-3.x^2-3.2xy-3.y^2$
    $= 4(x^2+xy+y^2)-3x^2-6xy-3y^2$

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

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