Question
Answer
$$(-7i-4)(-7i+4)=49i^2-16$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-7i-4)(-7i+4)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}49i^2-28i+28i-16 \xlongequal{ } \\[1 em] & \xlongequal{ }49i^2 -\cancel{28i}+ \cancel{28i}-16 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}49i^2-16\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-7i-4}\right) $ by each term in $ \left( -7i+4\right) $. $$ \left( \color{blue}{-7i-4}\right) \cdot \left( -7i+4\right) = 49i^2 -\cancel{28i}+ \cancel{28i}-16 $$ |
| ② | Combine like terms: $$ 49i^2 \, \color{blue}{ -\cancel{28i}} \,+ \, \color{blue}{ \cancel{28i}} \,-16 = 49i^2-16 $$ |
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