Question

Phân tích các đa thức sau thành nhân tử

a) x² - x - 6

b)x² + 4x² - 5

c)x³ - 19x - 30

Answer 1

a)  = x² - 3x + 2x - 6

    = x(x -3) + 2(x - 3)

    = (x - 3)(x + 2)

b)  = x² - x + 5x - 5

    = x(x - 1) + 5(x - 1)

    = (x - 1)(x + 5)

c)  = x³ - 5x² + 5x² - 25x + 6x - 30

    = x²(x - 5) + 5x(x - 5) +6(x - 5)

    = (x - 5)(x² + 5x + 6)

    = (x - 5)(x² + 2x + 3x + 6)

    = (x - 5)[x(x + 2) + 3(x + 2)]

    = (x - 5)(x + 2)(x + 3)

Answer 2

a)  = x² - 3x + 2x - 6

    = x(x -3) + 2(x - 3)

    = (x - 3)(x + 2)

b)  = x² - x + 5x - 5

    = x(x - 1) + 5(x - 1)

    = (x - 1)(x + 5)

c)  = x³ - 5x² + 5x² - 25x + 6x - 30

    = x²(x - 5) + 5x(x - 5) +6(x - 5)

    = (x - 5)(x² + 5x + 6)

    = (x - 5)(x² + 2x + 3x + 6)

    = (x - 5)[x(x + 2) + 3(x + 2)]

    = (x - 5)(x + 2)(x + 3)