$(5 - 4 i)^{2} = - 40 i + 9$

Explanation

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$(5 - 4 i)^{2} \overset{◯}{1} 25 - 40 i + 16 i^{2} \overset{◯}{2} 25 - 40 i - 16 \overset{◯}{3} - 40 i + 9$
①	Find $(5 - 4 i)^{2}$ using formula. $(A - B)^{2} = A^{2} - 2 \cdot A \cdot B + B^{2}$ where $A = 5$ and $B = 4 i$ . $(5 - 4 i)^{2} = 5^{2} - 2 \cdot 5 \cdot 4 i + (4 i)^{2} = 25 - 40 i + 16 i^{2}$
②	$16 i^{2} = 16 \cdot (- 1) = - 16$
③	Combine like terms: $- 40 i + 25 - 16 = - 40 i + 9$

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(5−4i)2=−40i+9

$(5 - 4 i)^{2} = - 40 i + 9$