$$5(-2x-3) = 9x+21$$

$$ \begin{aligned} 5(-2x-3) &= 9x+21&& \text{simplify left side} \\[1 em]-10x-15 &= 9x+21&& \text{move the $ \color{blue}{ 9x } $ to the left side and $ \color{blue}{ -15 }$ to the right} \\[1 em]-10x-9x &= 21+15&& \text{simplify left and right hand side} \\[1 em]-19x &= 36&& \text{ divide both sides by $ -19 $ } \\[1 em]x &= -\frac{36}{19}&& \\[1 em] \end{aligned} $$

This page was created using