What is i^78 + i^54 - i^59

i¹ = i
i² = -1
i³ = -i
i⁴ = 1

-1 - 1 + i
-2 - i

When adding exponants with the same base you just do simple addition or subtraction.

i^78 - i^-5 = i^73


Haha I'm wrong, sorry. Go with the other guy's answer.