Question
Answer
$$-x(x+4)(x-5)=-x^3+x^2+20x$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}-x(x+4)(x-5)& \xlongequal{ }-(x^2+4x)(x-5) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-(x^3-5x^2+4x^2-20x) \xlongequal{ } \\[1 em] & \xlongequal{ }-(x^3-x^2-20x) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-x^3+x^2+20x\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{x^2+4x}\right) $ by each term in $ \left( x-5\right) $. $$ \left( \color{blue}{x^2+4x}\right) \cdot \left( x-5\right) = x^3-5x^2+4x^2-20x $$ |
| ② | Remove the parentheses by changing the sign of each term within them. $$ - \left(x^3-x^2-20x \right) = -x^3+x^2+20x $$ |
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