Question
Answer
$$(x+9y)(x-4y)=x^2+5xy-36y^2$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(x+9y)(x-4y)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}x^2-4xy+9xy-36y^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}x^2+5xy-36y^2\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{x+9y}\right) $ by each term in $ \left( x-4y\right) $. $$ \left( \color{blue}{x+9y}\right) \cdot \left( x-4y\right) = x^2-4xy+9xy-36y^2 $$ |
| ② | Combine like terms: $$ x^2 \color{blue}{-4xy} + \color{blue}{9xy} -36y^2 = x^2+ \color{blue}{5xy} -36y^2 $$ |
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