The imaginary number ' i ' is the square root of -1.
i = √-1
i² = -1
i³ = -√-1
i to the 4th power = +1
i to the 5th power = √-1
etc.
and all the higher powers keep going in the same 4-step cycle.
What's 29 divided by 4 ?
It's 7 with a remainder of 1.
So 29 with all the 4s thrown away is 1, and ' i ' to the 29th power is
the same thing as ' i ' to the 1st power = √-1 or just plain ' i '.