Simplify 15i*4i

$15 i \cdot 4 i$

Multiply $15 i (4 i)$ .

Multiply $4$ by $15$ .

$60 i i$

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

$60 (i^{1} i)$

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

$60 (i^{1} i^{1})$

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

$60 i^{1 + 1}$

Add $1$ and $1$ .

$60 i^{2}$

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

$60 \cdot - 1$

Multiply $60$ by $- 1$ .

$- 60$