$$ \begin{aligned}(x+y)^2-5^2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}x^2+2xy+y^2-25\end{aligned} $$ | |
① | Find $ \left(x+y\right)^2 $ using formula. $$ (A + B)^2 = \color{blue}{A^2} + 2 \cdot A \cdot B + \color{red}{B^2} $$where $ A = \color{blue}{ x } $ and $ B = \color{red}{ y }$. $$ \begin{aligned}\left(x+y\right)^2 = \color{blue}{x^2} +2 \cdot x \cdot y + \color{red}{y^2} = x^2+2xy+y^2\end{aligned} $$$$ y^2 = 1^2y^2 = y^2 $$ |