x³ - 9x² + 7x + 1

= x³ - x2 - 8x² + 8x - x + 1

= (x³ - x²) - (8x² - 8x) - (x - 1)

= x²(x - 1) - 8x(x - 1) - (x - 1)

= (x - 1)(x² - 8x -1)

Ta có: \(\left(4x+1\right)\left(12x-1\right)\left(3x+2\right)\left(x+1\right)-4\)

\(=\left(12x^2+8x+3x+2\right)\left(12x^2+12x-x-1\right)-4\)

\(=\left(12x^2+11x+2\right)\left(12x^2+11x-1\right)-4\)

\(=\left(12x^2+11x\right)^2+\left(12x^2+11x\right)-6\)

\(=\left(12x^2+11x+3\right)\left(12x^2+11x-2\right)\)

7x-7y+ax-ay=(7x-7y)+(ax-ay)=7(x-y)+a(x-y)=(x-y)(7+a)

7x-7y+ax-ay

=(7x-7y)+(ax-ay)

=7(x-y)+a(x-y)

=(x-y)(7+a)

\(\left(x^2-3x\right)^2-14x^2+42x+40\\ =\left(x^2-3x-7\right)^2-9\\ =\left(x^2-3x-10\right)\left(x^2-3x-4\right)\)

\(\left(x^2-3x\right)^2-14x^2+42x+40\)

\(=\left(x^2-3x-4\right)\left(x^2-3x-10\right)\)

\(=\left(x-4\right)\left(x+1\right)\left(x-5\right)\left(x+2\right)\)

x²-2x-15=(x²-5x)+(3x-15)=x(x-5)+3(x-5)=(x-5)(x+3)

\(x^2-3x-15=\left(x^2-2.\dfrac{3}{2}x+\dfrac{9}{4}\right)-\dfrac{69}{4}=\left(x-\dfrac{3}{2}\right)^2-\left(\dfrac{\sqrt{69}}{2}\right)^2\)

\(=\left(x-\dfrac{3}{2}-\dfrac{\sqrt{69}}{2}\right)\left(x-\dfrac{3}{2}+\dfrac{\sqrt{69}}{2}\right)\)

\(x^2-2x-15=\left(x-5\right)\left(x+3\right)\)

\(x^3-3x^2-4x+12\)

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

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

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

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

\(x^3-3x^2-4x+12\)

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

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

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

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2x^4 - 2x^3 +9x^3 - 9x^2 +7x^2 -  7x - 6x + 6 = 2x^3(x-1)+9x^2(x-1)+7x(x-1)-6(x-1) = (x-1)(2x^3+9x^2+7x-6)                                               =(x-1)(x+2)(x+3)(2x-1)