Then the first power of I = I；; The quadratic of I =-1; The third power of I =-I; The fourth power of I = 1 ...

Therefore, we can know that the n power of I (n is a positive integer) is a periodic change with a period of 4, that is, when n=4k+b(k is an arbitrary integer, b=0, 1, 2, 3).

Then the (4k+b) power of I = the b power of I.