How do you simplify  (2 - i )( 4 + i )?

Jan 21, 2016

9 - 2i

Explanation:

Expand the brackets (distributive law - using FOIL method )

so (2 - i )(4 + i )

$= 8 + 2 i - 4 i - {i}^{2} = 8 - 2 i - {i}^{2} = 8 - 2 i + 1$

[ remembering that  i^2 = - 1 ]

$\Rightarrow \left(2 - i\right) \left(4 + i\right) = 9 - 2 i$