# write answer in both rectangular from and polar Q in degre

• Apr 23rd 2010, 08:00 AM
r-soy
write answer in both rectangular from and polar Q in degre
Hi

4 - write answer in both rectangular from and polar Q in degre

a ) (1 + i ) ( 2+ 2i )
b ) -2 + 2i
• Apr 23rd 2010, 11:26 AM
HallsofIvy
For the first one, you have written $(1+ i)(2+ 2i)= 2+ 2i+ 2i+2i^2$, which is correct but then you have that equal to 2+ 8i. $i^2= -1$ so that is equal to 2+ 4i- 2= 4i.

For the second, the angle, $3\pi/4$ is correct but "r" is wrong.
$2^2+ 2^2= 8= 4(2)$ and so $r= \sqrt{4(2)}= 2\sqrt{2}$. You have 2.8 which is approximately correct but unless you are specifically told to use a decmal approximation, $2\sqrt{2}$ is far better.