Question

Phân tích đa thức sau thành nhân tử:

a) \(x^4-10x^3-15x^2+20x+4\)

b) \(2x^4-5x^3-27x^2+25x+50\)

c) \(3x^4+6x^3-33x^2-24x+48\)

Answer 1

a) x⁴ - 10x³ - 15x² + 20x + 4

= x⁴ + 2x³ - 12x³ - 24x² + 9x² + 18x + 2x + 4

= x³(x + 2) - 12x²(x + 2) + 9x(x + 2) + 2(x + 2)

= (x + 2)(x³ - 12x² + 9x + 2)

b)

2x⁴ - 5x³ - 27x² + 25x + 50

= 2x³(x - 2) - x²(x - 2) - 25x(x - 2) - 25(x - 2)

= (x - 2)(2x³ - x² - 25x - 25)

Answer 2

c)\(3x^4+6x^3-33x^2-24x+48\)

\(=3\left(x^4+2x^3-11x^2-8x+16\right)\)

\(=3\left(x^4-x^3-4x^2+3x^3-3x^2-12x-4x^2+4x+16\right)\)

\(=3\left(x^2\left(x^2-x-4\right)+3x\left(x^2-x-4\right)-4\left(x^2-x-4\right)\right)\)

\(=3\left(x^2+3x-4\right)\left(x^2-x-4\right)\)

\(=3\left(x^2-x+4x-4\right)\left(x^2-x-4\right)\)

\(=3\left[x\left(x-1\right)+4\left(x-1\right)\right]\left(x^2-x-4\right)\)

\(=3\left(x-1\right)\left(x+4\right)\left(x^2-x-4\right)\)