a) Ta có: \(-5x^2+3x=0\)
\(\Leftrightarrow x\left(-5x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\-5x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\-5x=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\frac{3}{5}\end{matrix}\right.\)
Vậy: \(x\in\left\{0;\frac{3}{5}\right\}\)
b) Ta có: \(2-x=3\left(x+1\right)\)
\(\Leftrightarrow2-x=3x+3\)
\(\Leftrightarrow2-x-3x-3=0\)
\(\Leftrightarrow-1-4x=0\)
\(\Leftrightarrow-\left(1+4x\right)=0\)
\(\Leftrightarrow1+4x=0\)
\(\Leftrightarrow4x=-1\)
\(\Leftrightarrow x=\frac{-1}{4}\)
Vậy: \(x=\frac{-1}{4}\)
c) Ta có: \(4x+7\left(x-2\right)=-9x+5\)
\(\Leftrightarrow4x+7x-14+9x-5=0\)
\(\Leftrightarrow20x-19=0\)
\(\Leftrightarrow20x=19\)
\(\Leftrightarrow x=\frac{19}{20}\)
Vậy: \(x=\frac{19}{20}\)
d) Ta có: \(x^2+5x+4=0\)
\(\Leftrightarrow x^2+x+4x+4=0\)
\(\Leftrightarrow x\left(x+1\right)+4\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x+4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\x+4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=-4\end{matrix}\right.\)
Vậy: \(x\in\left\{-1;-4\right\}\)
