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