Question
Answer
$$(3-7i)^2=-42i-40$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(3-7i)^2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}9-42i+49i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}9-42i-49 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}-42i-40\end{aligned} $$ | |
| ① | Find $ \left(3-7i\right)^2 $ using formula. $$ (A - B)^2 = \color{blue}{A^2} - 2 \cdot A \cdot B + \color{red}{B^2} $$where $ A = \color{blue}{ 3 } $ and $ B = \color{red}{ 7i }$. $$ \begin{aligned}\left(3-7i\right)^2 = \color{blue}{3^2} -2 \cdot 3 \cdot 7i + \color{red}{\left( 7i \right)^2} = 9-42i+49i^2\end{aligned} $$ |
| ② | $$ 49i^2 = 49 \cdot (-1) = -49 $$ |
| ③ | Combine like terms: $$ -42i+ \color{blue}{9} \color{blue}{-49} = -42i \color{blue}{-40} $$ |
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