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

Aug 8, 2018

$98$

#### Explanation:

$\left(- 10 i\right) \left(9 i\right) + 8$

First, do multiplication:
$= - 90 {i}^{2} + 8$

We know that ${i}^{2}$ equals to $- 1$:
$= - 90 \left(- 1\right) + 8$

Simplify:
$= 90 + 8$

$= 98$

Hope this helps!

Aug 8, 2018

color(magenta)((-10i) * (9i) + 8 = 98

#### Explanation:

color(red)(i = sqrt(-1)), " " color(maroon)(i^2 = (sqrt-1)^2 = -1

$\left(- 10 i\right) \cdot \left(9 i\right) + 8 = \left(- 90 {i}^{2}\right) + 8 = \left(- 90 \cdot - 1\right) + 8$

$\implies 90 + 8 = 98$

Aug 8, 2018

$98$

#### Explanation:

We can multiply first to now get

$- 90 {i}^{2} + 8$

Recall that ${i}^{2} = - 1$. With this simplification, we now have

$90 + 8$, which simplifies to $98$.

Hope this helps!