Simplify (7i)(-9i)

$(7 i) (- 9 i)$

Step 1

Multiply $(7 i) (- 9 i)$ .

Multiply $- 9$ by $7$ .

$- 63 i i$

Raise $i$ to the power of $1$ .

$- 63 (i^{1} i)$

Raise $i$ to the power of $1$ .

$- 63 (i^{1} i^{1})$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$- 63 i^{1 + 1}$

Add $1$ and $1$ .

$- 63 i^{2}$

Step 2

Rewrite $i^{2}$ as $- 1$ .

$- 63 \cdot - 1$

Step 3

Multiply $- 63$ by $- 1$ .

$63$