To take the sum of -i and i, the operation that should be performed is addition.
`-i + i`
To add like terms, add the coefficients and copy the variable. Since there are no written numbers at the side of -i and i, it indicates that the coefficients are -1 and 1, respectively.
`= -1i + 1i`
Therefore, the sum of -i and i is zero.
`-i + i = 0`