What is i^35 + i^78

i¹ = i
i² = -1
i³ = -i
i⁴ = 1
i⁵ = i

-i - 1

i^1 = i
i^2 = -1
i^3 = -i
i^4 = 4



so i^x is mod4 in x

i^35 = (i^4)^8 i^3 = -i

i^78= (i^4)^19i^2 = 1

1-i is your answer