Question 241146
i is defined as the {{{sqrt(-1)}}}
So
i^1 = i
i^2 = -1
i^3 = -i
i^4 = (-1)(-1) = 1
And it repeats in a cycle of 4 
i^5 = i^4*i = 1+i = i
i^6 = i^4*i^2 = 1*i^2 = 1 *(-1) = -1
i^7 = i^4*i^3 = 1*i^3 = -i
etc etc

how do you use in a radical? If the value under the radical is negative, then look at that as (-1)*aPositive 
for instance {{{sqrt(-9) = sqrt((-1)*9) = sqrt(-1)*sqrt(9)}}} = plus or minus 3i