Answer
$$(x+4)(x-1)(2x+5)=2x^3+11x^2+7x-20$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(x+4)(x-1)(2x+5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}(x^2-x+4x-4)(2x+5) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}(x^2+3x-4)(2x+5) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}2x^3+5x^2+6x^2+15x-8x-20 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}2x^3+11x^2+7x-20\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{x+4}\right) $ by each term in $ \left( x-1\right) $. $$ \left( \color{blue}{x+4}\right) \cdot \left( x-1\right) = x^2-x+4x-4 $$ |
| ② | Combine like terms: $$ x^2 \color{blue}{-x} + \color{blue}{4x} -4 = x^2+ \color{blue}{3x} -4 $$ |
| ③ | Multiply each term of $ \left( \color{blue}{x^2+3x-4}\right) $ by each term in $ \left( 2x+5\right) $. $$ \left( \color{blue}{x^2+3x-4}\right) \cdot \left( 2x+5\right) = 2x^3+5x^2+6x^2+15x-8x-20 $$ |
| ④ | Combine like terms: $$ 2x^3+ \color{blue}{5x^2} + \color{blue}{6x^2} + \color{red}{15x} \color{red}{-8x} -20 = 2x^3+ \color{blue}{11x^2} + \color{red}{7x} -20 $$ |
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