Simplify your answer completely: $5i(1 + i)^2$ Simplify your answer completely: $5i(1 + i)^2$ I know the answer is $-10$, but I don't know how to get it. Things I tried: foiling $(1+i)^2$ and then distributing $5i$. distributing $5i$ into $(1+i)$ and then foiling

Since $$(a+b)^2=a^2+2ab+b^2,$$ one has$$5i(1+i)^2=5i(1^2+2\cdot 1\cdot i+i^2)=5i(1+2i-1)=5i\cdot 2i=-10.$$