Powers of i are "periodic with period 4". That is, , , , , and and now everything repeasts.

4 divides into 15 3 times with remainder 3: 3(4)+ 3= 12+ 3= 15. That means that .

7= 4+ 3 and 11= 4+ 4+ 3 so and . Theydon't"both = 0". They both equal -i so their difference is 0.