Tap the blue circles to see an explanation.
$$ \begin{aligned}(x-9)(x+1)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}x^2+x-9x-9 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}x^2-8x-9\end{aligned} $$ | |
① | Multiply each term of $ \left( \color{blue}{x-9}\right) $ by each term in $ \left( x+1\right) $. $$ \left( \color{blue}{x-9}\right) \cdot \left( x+1\right) = x^2+x-9x-9 $$ |
② | Combine like terms: $$ x^2+ \color{blue}{x} \color{blue}{-9x} -9 = x^2 \color{blue}{-8x} -9 $$ |