平方完成計算機

Your input: complete the square in $$$x^{2} + 4 x$$$.

Add and subtract $$$4$$$:

$$$x^{2} + 4 x=x^{2} + 4 x + {\color{red}{\left(4\right)}} - {\color{red}{\left(4\right)}}$$$

Complete the square:

$$$-4 + {\color{red}{\left(x^{2} + 4 x + 4\right)}}=-4 + {\color{red}{\left(x + 2\right)^{2}}}$$$

Answer: $$$x^{2} + 4 x=\left(x + 2\right)^{2} - 4$$$.