Value of "i"

 i = sqrt(-1), which is an impossibility because there is no square root of any negative number.

Like RS said  'i' is DEFINED as sqrt(-1)     Many times you will have problems like  sqrt(-4)   to simplify this we will often use 'i'     sqrt(-4)  =  sqrt(4 * (-1))  =  2 sqrt(-1) = 2i      Ya see???

Then i^2 = -1     i^3 = -i