Hi

I want check my answer

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

a ) (1 + i ) ( 2+ 2i )

b ) -2 + 2i

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- Apr 23rd 2010, 08:00 AMr-soywrite answer in both rectangular from and polar Q in degre
Hi

I want check my answer

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 AMHallsofIvy
For the first one, you have written $\displaystyle (1+ i)(2+ 2i)= 2+ 2i+ 2i+2i^2$, which is correct but then you have that equal to 2+ 8i. $\displaystyle i^2= -1$ so that is equal to 2+ 4i- 2= 4i.

For the second, the angle, $\displaystyle 3\pi/4$ is correct but "r" is wrong.

$\displaystyle 2^2+ 2^2= 8= 4(2)$ and so $\displaystyle r= \sqrt{4(2)}= 2\sqrt{2}$. You have 2.8 which is approximately correct but unless you are specifically told to use a decmal approximation, $\displaystyle 2\sqrt{2}$ is far better.