Solve this:
9. Express i9 + i10 + i11 + i12 in the form of a+ib
in for n>4,divide n by 4 and obtain the remainder r, the value of in for n>4 is ir.
i9 = i
i10= (-1)
i11= (-i)
i12= 1
i+(-1)+(-i)+1=0
i9 = i
i10= (-1)
i11= (-i)
i12= 1
i+(-1)+(-i)+1=0