Answer
$$(x+5)(x^2+4x-8)=x^3+9x^2+12x-40$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(x+5)(x^2+4x-8)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}x^3+4x^2-8x+5x^2+20x-40 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}x^3+9x^2+12x-40\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{x+5}\right) $ by each term in $ \left( x^2+4x-8\right) $. $$ \left( \color{blue}{x+5}\right) \cdot \left( x^2+4x-8\right) = x^3+4x^2-8x+5x^2+20x-40 $$ |
| ② | Combine like terms: $$ x^3+ \color{blue}{4x^2} \color{red}{-8x} + \color{blue}{5x^2} + \color{red}{20x} -40 = x^3+ \color{blue}{9x^2} + \color{red}{12x} -40 $$ |
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