Question

Bài 1 rút gọn

a) (x+3)(x-3)-(x-3)²

b) (2x+1)²+2(2x+1)(x-1)+(x-1)²

^{c) x(x-3)(x+3)-(x^2 +1)(x^2-1)}

Bài 2 tìm x

a) (x+2)²-x^2-3x=21

b) x^2+x-12=0

c) x^3-3x^2+3x-126=0

d) x^3-5x^2+8x-4=0

e) 2x^3-x^2+3x+6=0

f) (x^2+x) (x^2+x+1)=6

Answer 1

1.

a, \(\left(x+3\right)\left(x-3\right)-\left(x-3\right)^2\)

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

\(=9\left(x-3\right)=9x-27\)

b, \(\left(2x+1\right)^2+2\left(2x+1\right)\left(x-1\right)+\left(x-1\right)^2\)

\(=\left(2x+1+x-1\right)^2=9x^2\)

c, \(x\left(x-3\right)\left(x+3\right)-\left(x^2+1\right)\left(x^2-1\right)\)

\(=x\left(x^2-9\right)-\left(x^4-1\right)\)

\(=x^3-9x-x^4+1=-x^4+x^3-9x+1\)

Answer 2

bài 2a)

\(\left(x+2\right)^2-x^2-3x=21\)

\(\left(x+2-x\right).\left(x+2+x\right)-3x=21\)

\(\left(x-x+2\right).\left(x+x+2\right)-3x=21\)

\(2.\left(2x+2\right)-3x=21\)

\(4x+2.2-3x=21\)

\(4x+4-3x=21\)

\(4x-3x=21-4\)

\(x=17\)