| $$ \begin{aligned}(3x-1)^3& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}27x^3-27x^2+9x-1\end{aligned} $$ | |
| ① | Find $ \left(3x-1\right)^3 $ using formula $$ (A - B) = A^3 - 3A^2B + 3AB^2 - B^3 $$where $ A = 3x $ and $ B = 1 $. $$ \left(3x-1\right)^3 = \left( 3x \right)^3-3 \cdot \left( 3x \right)^2 \cdot 1 + 3 \cdot 3x \cdot 1^2-1^3 = 27x^3-27x^2+9x-1 $$ |