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

Toán Lớp 8: phân tích đa thức thành nhân tử: x^3-19x-30

Toán Lớp 8: phân tích đa thức thành nhân tử:
x^3-19x-30

Comments ( 2 )

  1. \qquad x^3-19x-30
    =x^3-5x^2+5x^2-25x+6x-30
    =x^2(x-5)+5x(x-5)+6(x-5)
    =(x-5)(x^2+5x+6)
    =(x-5)(x^2+2x+3x+6)
    =(x-5)[x(x+2)+3(x+2)]
    =(x-5)(x+2)(x+3)

  2. x^3 – 19x – 30
    = x^3 + 5x^2 + 6x – 5x^2 – 25x – 30
    = x(x^2 + 5x + 6) – 5(x^2 + 5x + 6)
    = (x-5)(x^2 + 5x + 6)
    = (x-5)(x^2 + 2x + 3x + 6)
    = (x-5)[x(x+2) + 3(x+2)]
    = (x-5)(x+3)(x+2)

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