Question

(x+7)² -3x-21=0

Answer 1

\(\left(x+7\right)^2-3x-21=0\\ =>\left(x+7\right)^2-3\left(x+7\right)=0\\ =>\left(x+7\right)\left(x+7-3\right)=0\\ =>\left(x+7\right)\left(x+4\right)=0\\ =>\left[{}\begin{matrix}x+7=0\\x+4=0\end{matrix}\right.=>\left[{}\begin{matrix}x=-7\\x=-4\end{matrix}\right.\)