a) Ta có: \(5x\left(x+1\right)-5\left(x+1\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left[5x-5\left(x-2\right)\right]=0\)
\(\Leftrightarrow\left(x+1\right)\left(5x-5x+10\right)=0\)
\(\Leftrightarrow10\left(x+1\right)=0\)
mà \(10\ne0\)
nên x+1=0
hay x=-1
Vậy: x=-1
b) Ta có: \(\left(4x+1\right)\left(x-2\right)-\left(2x-3\right)=4\)
\(\Leftrightarrow4x^2-8x+x-2-2x+3-4=0\)
\(\Leftrightarrow4x^2-9x-3=0\)
\(\Leftrightarrow\left(2x\right)^2-2\cdot2x\cdot\frac{9}{4}+\frac{81}{16}-\frac{129}{16}=0\)
\(\Leftrightarrow\left(2x-\frac{9}{4}\right)^2=\frac{129}{16}\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-\frac{9}{4}=\frac{\sqrt{129}}{4}\\2x-\frac{9}{4}=-\frac{\sqrt{129}}{4}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=\frac{9+\sqrt{129}}{4}\\2x=\frac{9-\sqrt{129}}{4}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{9+\sqrt{129}}{8}\\x=\frac{9-\sqrt{129}}{8}\end{matrix}\right.\)
Vậy: \(x\in\left\{\frac{9+\sqrt{129}}{8};\frac{9-\sqrt{129}}{8}\right\}\)
c) Ta có: \(2x^3-18x=0\)
\(\Leftrightarrow2x\left(x^2-9\right)=0\)
\(\Leftrightarrow2x\left(x-3\right)\left(x+3\right)=0\)
mà \(2\ne0\)
nên \(\left[{}\begin{matrix}x=0\\x+3=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-3\\x=3\end{matrix}\right.\)
Vậy: \(x\in\left\{0;-3;3\right\}\)
d) Ta có: \(\left(3x-2\right)\left(2x+1\right)-6x\left(x+2\right)=11\)
\(\Leftrightarrow6x^2+3x-4x-2-6x^2-12x=11\)
\(\Leftrightarrow-13x-2=11\)
\(\Leftrightarrow-13x=13\)
hay x=-1
Vậy: x=-1
e) Ta có: \(\left(x-1\right)^3-\left(x+2\right)\left(x^2-2x+4\right)=3\left(1-x^2\right)\)
\(\Leftrightarrow x^3-3x^2+3x-1-\left(x^3+8\right)=3-3x^2\)
\(\Leftrightarrow x^3-3x^2+3x-1-x^3-8-3+3x^2=0\)
\(\Leftrightarrow3x-12=0\)
\(\Leftrightarrow3x=12\)
hay x=4
Vậy: x=4
f) Ta có: \(6x^2-\left(2x+5\right)\left(3x-2\right)=-1\)
\(\Leftrightarrow6x^2-\left(6x^2-4x+15x-10\right)+1=0\)
\(\Leftrightarrow6x^2-6x^2+4x-15x+10+1=0\)
\(\Leftrightarrow-11x+11=0\)
\(\Leftrightarrow-11x=-11\)
hay x=1
Vậy: x=1
