# 3i*7i

Simplify the imaginary number product 3i*7i

__Group coefficients and add powers of i__

(3 * 7)i^{(1 + 1)} = 21i^{2}

We need to evaluate and simplify 21i^{2} where i = √-1

i^{2} = √-1 * √-1

i^{2} = (√-1)^{2}

i^{2} = -1

__Multiply our result by our coefficient of 21__

21(-1) = **-21**