$(3 - 7 i)^{2} = - 42 i - 40$

Explanation

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$(3 - 7 i)^{2} \overset{◯}{1} 9 - 42 i + 49 i^{2} \overset{◯}{2} 9 - 42 i - 49 \overset{◯}{3} - 42 i - 40$
①	Find $(3 - 7 i)^{2}$ using formula. $(A - B)^{2} = A^{2} - 2 \cdot A \cdot B + B^{2}$ where $A = 3$ and $B = 7 i$ . $(3 - 7 i)^{2} = 3^{2} - 2 \cdot 3 \cdot 7 i + (7 i)^{2} = 9 - 42 i + 49 i^{2}$
②	$49 i^{2} = 49 \cdot (- 1) = - 49$
③	Combine like terms: $- 42 i + 9 - 49 = - 42 i - 40$

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(3−7i)2=−42i−40

$(3 - 7 i)^{2} = - 42 i - 40$