+0  
 
0
37
2
avatar

Multiply and simplify the following complex numbers: (1 + 2i) x (1 - 4i)

 Apr 19, 2020
 #1
avatar+367 
+2

Hi guest!
 

We can start off by multiplying the pairs together:

1*1=1

1*-4i=-4i

2i*1=2i

2i*-4i=\(-8i^2\). We know that i^2 = -1. So -8i^2 = -8*-1=8

 

Now, let's add these all together.

1-4i+2i+8 = 9-2i.

 

I hope this helped you!

:)

 Apr 19, 2020
 #2
avatar+44 
+2

FOIL, yeilds,  1 - 4i + 2i - 8i^2 and then i^2 = -1.

1 - 4i + 2i + 8, combining like terms, 9 - 2i is the final complex number

 Apr 19, 2020

46 Online Users

avatar
avatar
avatar
avatar