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

Toán Lớp 8: (x+3)(x^2+2xy+4y^2) (x-2y)(x^2+2xy+4y^2

Toán Lớp 8: (x+3)(x^2+2xy+4y^2)

(x-2y)(x^2+2xy+4y^2

Comments ( 2 )

  1. (x+3)(x^2 + 2xy + 4y^2)
    = x . x^2 + x . 2xy + x . 4y^2 + 3 . x^2 + 3 . 2xy + 3 . 4y^2
    =  x^3 + 2x^2y + 4xy^2 + 3x^2 + 6xy + 12y^2
    (x-2y)(x^2 + 2xy + 4y^2)
    = (x-2y) . [ x^2 + x . 2y + (2y)^2]
    = x^3 – (2y)^3
    = x^3 – 8y^3

  2. a)
    (x+3)(x^2+2xy+4y^2)
    =x.x^2+x.2xy+x.4y^2+3.x^2+3.2xy+3.4y^2
    =x^3+2x^3y+4xy^2+3x^2+6xy+12y^2
    b)
    (x-2y)(x^2+2xy+4y^2)
    =x.x^2+x.2xy+x.4y^2-2y.x^2-2y.2xy-2y.4y^2
    =x^3+2x^2y+4xy^2-2x^2y-4xy^2-8y^3
    =x^3-8y^3
     

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