\(a,4x^2-25=0\)
\(\Leftrightarrow\left(2x-5\right)\left(2x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-5=0\\2x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}\\x=-\dfrac{5}{2}\end{matrix}\right.\)
\(b,2x^2+9x=0\)
\(\Leftrightarrow x\left(2x+9\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\2x+9=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-\dfrac{9}{2}\end{matrix}\right.\)
\(c,x^2+x-30=0\)
\(\Leftrightarrow x^2+6x-5x-30=0\)
\(\Leftrightarrow x\left(x+6\right)-5\left(x+6\right)=0\)
\(\Leftrightarrow\left(x-5\right)\left(x+6\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-6\end{matrix}\right.\)
\(d,2x^2-3x-5=0\)
\(\Leftrightarrow2x^2-5x+2x-5=0\)
\(\Leftrightarrow x\left(2x-5\right)+\left(2x-5\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(2x-5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\2x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\dfrac{5}{2}\end{matrix}\right.\)
