Question

Tìm x biết:

a) (x-3).(x²+3x+9) + (x+2).(2-x) = 1

b) x³-8-(x-2).(x²+3) = 0

c) (2x+1)³-(x-2)³ = 0

Answer 1

a: Sửa đề: \(\left(x-3\right)\left(x^2+3x+9\right)+x\left(x+2\right)\left(2-x\right)=1\)

\(\Leftrightarrow x^3-27-x\left(x^2-4\right)=1\)

=>4x-27=1

hay x=7

b: \(x^3-8-\left(x-2\right)\left(x^2+3\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x^2+2x+4\right)-\left(x-2\right)\left(x^2+3\right)=0\)

=>(x-2)(2x+1)=0

=>x=-1/2 hoặc x=2

c: \(\Leftrightarrow\left(2x+1-x+2\right)\left[\left(4x^2+4x+1\right)+\left(2x+1\right)\left(x-2\right)+\left(x-2\right)^2\right]=0\)

=>x+3=0

hay x=-3