# Complex numbers question

• Aug 3rd 2010, 04:09 AM
blackdragon190
Complex numbers question
I'm completely stuck on this one question:

Find real x and y for which x - y +2(x + y - 1)i = 5 + 4i

Can someone go through it with me or give me a hint..?
• Aug 3rd 2010, 04:27 AM
Plato
Quote:

Originally Posted by blackdragon190
Findd real x and y for which x - y +2(x + y - 1)i = 5 + 4i[/I]
Can someone go through it with me or give me a hint..?

Solve this system: $\displaystyle \left\{ \begin{gathered} x - y = 5 \hfill \\ x + y - 1 = 2 \hfill \\ \end{gathered} \right.$
• Aug 3rd 2010, 05:11 AM
blackdragon190
Thanks :) But how did you get those equations?
• Aug 3rd 2010, 05:34 AM
eumyang
You equate the real and imaginary parts of the 2 complex numbers. If you look at
$\displaystyle x - y + 2(x + y - 1)i = 5 + 4i$
On the left side, x - y is the real part (no i), and on the right side, 5 is the real part. So you set them equal to each other:
$\displaystyle x - y = 5$

Look at the imaginary parts. On the left side you have 2(x + y - 1), and on the right side you have 4. So they're equal:
$\displaystyle 2(x + y - 1) = 4$

You can simplify a little bit by dividing both sides by 2:
$\displaystyle x + y - 1 = 2$

So now you have the system that Plato wrote above.
• Aug 3rd 2010, 02:24 PM
blackdragon190
Oh, I get it now. Thanks!