Question

question 20
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simplify the following expression
(-18i).(-5i)= enter your answer
if the answer is complex use i to denote i.
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Explanation:

Step1: Multiply the coefficients

$(-18)\times(-5)=90$

Step2: Multiply the imaginary - parts

$i\times i = i^{2}$
Since $i^{2}=-1$, then $90\times i^{2}=90\times(-1)= - 90$

Answer:

$-90$