Question
Answer
$$-x(x+3)(x-3)=-x^3+9x$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}-x(x+3)(x-3)& \xlongequal{ }-(x^2+3x)(x-3) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-(x^3-3x^2+3x^2-9x) \xlongequal{ } \\[1 em] & \xlongequal{ }-(x^3-9x) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-x^3+9x\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{x^2+3x}\right) $ by each term in $ \left( x-3\right) $. $$ \left( \color{blue}{x^2+3x}\right) \cdot \left( x-3\right) = x^3 -\cancel{3x^2}+ \cancel{3x^2}-9x $$ |
| ② | Remove the parentheses by changing the sign of each term within them. $$ - \left(x^3-9x \right) = -x^3+9x $$ |
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