Precalculus: Mathematics for Calculus, 7th Edition

$a)$ $-3-2i$ $b)$ $2+8i$
$a)$ $(3-6i)-(6-4i)$ Evaluate the subtraction: $(3-6i)-(6-4i)=(3-6)+(-6+4)i=-3-2i$ $b)$ $4i(2-\frac{1}{2}i)$ Evaluate the product: $4i\Big(2-\dfrac{1}{2}i\Big)=8i-2i^{2}=...$ Substitute $i^{2}$ by $-1$ and simplify if possible: $...=8i-2(-1)=2+8i$