(8-7i)(8-7i)=(8-7i)^2

by (a-b)^2=a^2+b^2-2*a*b

(8-7i)^2=8^2+(7i)^2-2*8*7i

           =64+49(-1)-112i

           =64-49-112i

           =15-112i

this should be the answer