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