Tap the blue circles to see an explanation.
$$ \begin{aligned}(r-2)(r^2+128)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}r^3+128r-2r^2-256 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}r^3-2r^2+128r-256\end{aligned} $$ | |
① | Multiply each term of $ \left( \color{blue}{r-2}\right) $ by each term in $ \left( r^2+128\right) $. $$ \left( \color{blue}{r-2}\right) \cdot \left( r^2+128\right) = r^3+128r-2r^2-256 $$ |
② | Combine like terms: $$ r^3-2r^2+128r-256 = r^3-2r^2+128r-256 $$ |