Question

I : PTĐTTNT

a)A= (x-1)(x+2)(x+7)-16

b) A= \(\left(x^2-x-2\right)^2+\left(x-2\right)^2\)

c) \(81x^4+4\)

d) \(\left(x^2-3\right)^2+16\)

help me

Answer 1

a) \(A=\left(x^2+x-2\right)\left(x+7\right)-16\)

\(=x^3+8x^2+5x-14-16\)

\(=x^3+8x^2+5x-30\)

\(=x^3+3x^2+5x^2+15x-10x-30\)

\(=x^2\left(x+3\right)+5x\left(x+3\right)-10\left(x+3\right)\)

\(=\left(x^2+5x-10\right)\left(x+3\right)\)

b) \(A=x^4-2x^3-3x^2+4x+4+x^2-4x+4\)

\(=x^4-2x^3-2x^2+8\)

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

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

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

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

c) \(81x^4+4=81x^4+36x^2+4-36x^2\)

\(=\left(9x^2+2\right)^2-\left(6x\right)^2\)

\(=\left(9x^2-6x+2\right)\left(9x^2+6x+2\right)\)

d) \(\left(x^2-3\right)^2+16=x^4-6x^2+25\)

\(=\left(x^4+10x^2+25\right)-16x^2\)

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

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

Answer 2

sửa câu b) xíu nha!

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

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

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