Question
Answer
$$(-1-3x)^3=-27x^3-27x^2-9x-1$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-1-3x)^3& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-1-9x-27x^2-27x^3 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-27x^3-27x^2-9x-1\end{aligned} $$ | |
| ① | Find $ \left(-1-3x\right)^3 $ using formula $$ (A - B) = A^3 - 3A^2B + 3AB^2 - B^3 $$where $ A = -1 $ and $ B = 3x $. $$ \left(-1-3x\right)^3 = \left( -1 \right)^3-3 \cdot \left( -1 \right)^2 \cdot 3x + 3 \cdot \left( -1 \right) \cdot \left( 3x \right)^2-\left( 3x \right)^3 = -1-9x-27x^2-27x^3 $$ |
| ② | Combine like terms: $$ -27x^3-27x^2-9x-1 = -27x^3-27x^2-9x-1 $$ |
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