# How do you multiply (6-3i)(3-i)?

Sep 12, 2016

$15 - 15 i$

#### Explanation:

distribute the brackets using, for example, the FOIL method.

$\Rightarrow \left(6 - 3 i\right) \left(3 - i\right) = 18 - 6 i - 9 i + 3 {i}^{2} = 18 - 15 i + 3 {i}^{2}$

$\textcolor{\mathmr{and} a n \ge}{\text{Reminder }}$

$\textcolor{red}{\overline{\underline{| \textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{{i}^{2} = {\left(\sqrt{- 1}\right)}^{2} = - 1} \textcolor{w h i t e}{\frac{a}{a}} |}}}$

$\Rightarrow 18 - 15 i + 3 {i}^{2} = 18 - 15 i - 3 = 15 - 15 i$

$\Rightarrow \left(6 - 3 i\right) \left(3 - i\right) = 15 - 15 i$