First thing to do is expand , then re-write the result as and find and
If x1 + iy1 is an element of C and has an absolute value r1 and argument phi1, and
x2 + iy2 is an element of C and has absolute value r2 and argument phi2, then
the product (x1 + iy1)(x2 + iy2) has absolute value r1r2 and argument (one among many) phi1 + phi2
where C is the set of complex numbers. Any help would be appreciated for this proof!