# How do you simplify (-10i)(-9i)-(8i)(6+9i)?

Oct 10, 2016

$\left(- 10 i\right) \times \left(- 9 i\right) - 8 i \left(6 + 9 i\right) = - 18 - 48 i$

#### Explanation:

$\left(- 10 i\right) \times \left(- 9 i\right) - 8 i \left(6 + 9 i\right) = \left(- 9 \times - 10\right) {i}^{2} - 48 i - 72 {i}^{2}$

And so, $\left(- 9 \times - 10\right) {i}^{2} - 48 i - 72 {i}^{2}$

$=$ $18 {i}^{2} - 48 i$

Of course, we know that ${i}^{2} = - 1$

Thus, $18 {i}^{2} - 48 i$

$=$ $- 18 - 48 i$