Question

Tìm x biết:

a)3x(x-5)+2(5-x)=0

b)(x+2)^3-x^2(x-6)=4

Answer 1

a) \(\Rightarrow3x\left(x-5\right)-2\left(x-5\right)=0\)

\(\Rightarrow\left(x-5\right)\left(3x-2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=5\\x=\dfrac{2}{3}\end{matrix}\right.\)

b) \(\Rightarrow x^3+6x^2+12x+8-x^3+6x^2=4\)

\(\Rightarrow12x^2+12x+4=0\)

\(\Rightarrow x\in\varnothing\)(do \(12x^2+12x+4=12\left(x^2+x+\dfrac{1}{4}\right)+1=12\left(x+\dfrac{1}{2}\right)^2+1\ge1>0\))