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# Help

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How do you find the power for (12i-5)^2 in rectangular form? i represent imaginary number. Thanks

Feb 25, 2019

#1
+23827
+3

How do you find the power for $$(12i-5)^2$$ in rectangular form?

I represent imaginary number.

$$\begin{array}{|rcll|} \hline && (12i-5)^2 \\ &=& (12i)^2 -2\cdot 12i \cdot 5 + 5^2 \\ &=& 12^2i^2 -10\cdot 12i + 25 \\ &=& 144i^2 -120i + 25 \\ &=& 144i^2+25 -120i \quad | \quad i^2 = -1 \\ &=& 144(-1)+25 -120i \\ &=& -144+25 -120i \\ \mathbf{(12i-5)^2} &\mathbf{=}& \mathbf{-119 -120i} \\ \hline \end{array}$$

Feb 25, 2019

#1
+23827
+3

How do you find the power for $$(12i-5)^2$$ in rectangular form?

I represent imaginary number.

$$\begin{array}{|rcll|} \hline && (12i-5)^2 \\ &=& (12i)^2 -2\cdot 12i \cdot 5 + 5^2 \\ &=& 12^2i^2 -10\cdot 12i + 25 \\ &=& 144i^2 -120i + 25 \\ &=& 144i^2+25 -120i \quad | \quad i^2 = -1 \\ &=& 144(-1)+25 -120i \\ &=& -144+25 -120i \\ \mathbf{(12i-5)^2} &\mathbf{=}& \mathbf{-119 -120i} \\ \hline \end{array}$$

heureka Feb 25, 2019