Question
Answer
$$3x(-x+5)(x+1)=-3x^3+12x^2+15x$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}3x(-x+5)(x+1)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}(-3x^2+15x)(x+1) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-3x^3-3x^2+15x^2+15x \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}-3x^3+12x^2+15x\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{3x} $ by $ \left( -x+5\right) $ $$ \color{blue}{3x} \cdot \left( -x+5\right) = -3x^2+15x $$ |
| ② | Multiply each term of $ \left( \color{blue}{-3x^2+15x}\right) $ by each term in $ \left( x+1\right) $. $$ \left( \color{blue}{-3x^2+15x}\right) \cdot \left( x+1\right) = -3x^3-3x^2+15x^2+15x $$ |
| ③ | Combine like terms: $$ -3x^3 \color{blue}{-3x^2} + \color{blue}{15x^2} +15x = -3x^3+ \color{blue}{12x^2} +15x $$ |
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