Question
Answer
$$21-i-(9-i)=12$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}21-i-(9-i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}21-i-9+i \xlongequal{ } \\[1 em] & \xlongequal{ }21 -\cancel{i}-9+ \cancel{i} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}12\end{aligned} $$ | |
| ① | Remove the parentheses by changing the sign of each term within them. $$ - \left( 9-i \right) = -9+i $$ |
| ② | Combine like terms: $$ \color{blue}{21} \, \color{red}{ -\cancel{i}} \, \color{blue}{-9} + \, \color{red}{ \cancel{i}} \, = \color{blue}{12} $$ |
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