Question

Which expression is equivalent to (4 + 6i)2?

Answer 1

$\bf \textit{recall that }i^2=-1\\\\ -------------------------------\\\\ (4+6i)^2\implies (4+6i)(4+6i)\implies 16+24i+24i+36i^2 \\\\\\ 16+48i+36(-1)\implies 16+48i-36\implies -20+48i$

Answer 2

If you mean $(4+6i)^2$ then
remember that $i=\sqrt{-1}$ and that $i^2=-1$
just treat 'i' as a variable for the expansion part
$(4+6i)^2=$$(4+6i)(4+6i)=$$(4*4)+(6i*4)+(4*6i)+(6i*6i)=$$16+24i+24i+36i^2=$$16+48i+36(-1)=$$16+48i-36=$$-20+48i$
you didn't give us the expressions so you will have to see which one of them is equivilent ot -20+48i