\(a,x^2+4x=-3\Leftrightarrow x^2+4x+3=0\Leftrightarrow\left(x+1\right)\left(x+3\right)=0\)
\(\left[{}\begin{matrix}x=-1\\x=-3\end{matrix}\right.\)
\(b,3x^2+4x-4=0\Leftrightarrow3x^2+6x-2x-4=0\Leftrightarrow3x\left(x+2\right)-2\left(x+2\right)=0\Leftrightarrow\left(3x-2\right)\left(x+2\right)=0\)
\(\left[{}\begin{matrix}x=-2\\3x=2\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-2\\x=\frac{2}{3}\end{matrix}\right.\)
\(c,x^2+5x-6=0\Leftrightarrow\left(x-1\right)\left(x+6\right)=0\)
\(\left[{}\begin{matrix}x=1\\x=-6\end{matrix}\right.\)
\(d,x^2-6x=-9\Leftrightarrow x^2+6x+9=0\Leftrightarrow\left(x-3\right)^2=0\Leftrightarrow x-3=0\Leftrightarrow x=3\)