Answer
$$(2-i)^4=-24i-7$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(2-i)^4& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}i^4-8i^3+24i^2-32i+16 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle5}{\textcircled {5}} \htmlClass{explanationCircle explanationCircle6}{\textcircled {6}} \htmlClass{explanationCircle explanationCircle7}{\textcircled {7}} } }}}1+8i-24-32i+16 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle8}{\textcircled {8}} } }}}-24i-7\end{aligned} $$ | |
| ① | $$ (2-i)^4 = (2-i)^2 \cdot (2-i)^2 $$ |
| ② | Find $ \left(2-i\right)^2 $ using formula. $$ (A - B)^2 = \color{blue}{A^2} - 2 \cdot A \cdot B + \color{red}{B^2} $$where $ A = \color{blue}{ 2 } $ and $ B = \color{red}{ i }$. $$ \begin{aligned}\left(2-i\right)^2 = \color{blue}{2^2} -2 \cdot 2 \cdot i + \color{red}{i^2} = 4-4i+i^2\end{aligned} $$ |
| ③ | Multiply each term of $ \left( \color{blue}{4-4i+i^2}\right) $ by each term in $ \left( 4-4i+i^2\right) $. $$ \left( \color{blue}{4-4i+i^2}\right) \cdot \left( 4-4i+i^2\right) = 16-16i+4i^2-16i+16i^2-4i^3+4i^2-4i^3+i^4 $$ |
| ④ | Combine like terms: $$ 16 \color{blue}{-16i} + \color{red}{4i^2} \color{blue}{-16i} + \color{green}{16i^2} \color{orange}{-4i^3} + \color{green}{4i^2} \color{orange}{-4i^3} +i^4 = \\ = i^4 \color{orange}{-8i^3} + \color{green}{24i^2} \color{blue}{-32i} +16 $$ |
| ⑤ | $$ i^4 = i^2 \cdot i^2 =
( - 1) \cdot ( - 1) =
1 $$ |
| ⑥ | $$ -8i^3 = -8 \cdot \color{blue}{i^2} \cdot i =
-8 \cdot ( \color{blue}{-1}) \cdot i =
8 \cdot \, i $$ |
| ⑦ | $$ 24i^2 = 24 \cdot (-1) = -24 $$ |
| ⑧ | Combine like terms: $$ \color{blue}{8i} \color{blue}{-32i} \color{red}{-24} + \color{green}{1} + \color{green}{16} = \color{blue}{-24i} \color{green}{-7} $$ |
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