The Student Room Group
Reply 1
a411a2900=(a2+25)(a236)a^4-11a^2-900=(a^2+25)(a^2-36)
Reply 2
On 1) expand the brackets and look at the real and imaginary parts separately.
(edited 13 years ago)
Reply 3
On 1) expand the bracket and look at the real and imaginary parts separately.


Yeah I did that and got to 2x - 8 = i3y + ix
I didn't know what to do after that, guessing it's something simple?
Reply 4
Original post by Erotas
1) The real and imaginary parts of the complex number z = x + iy satisfy the equation (2-i)x - (1+3i)y - 7 = 0.

Find the value of x and the value of y.

And for another question I have to solve a^4 - 11a^2 - 900=0
Is there a quick way to do this because I used trial and error which took forever.

Any help is much appreciated!


1. Expand out the brackets and you'll get f(x,y) + g(x,y)i = 0. 0 is the same as 0+0i, so you can set f=0 and g=0 and solve as simultaneous equations.

2. If you look carefully this is just a quadratic, if you use the substitution x = a^2 then this should become something you're used to. Just remember to put a^2 back in at the end (or before solving will be easier in this case).

Any questions, quote me and I'll answer them.
Reply 5
Original post by Erotas
Yeah I did that and got to 2x - 8 = i3y + ix
I didn't know what to do after that, guessing it's something simple?


You need to check that expansion (or the question you have typed on here).
Reply 6
You need to check that expansion (or the question you have typed on here).


Misread the y as a 1 :tongue: so the expansion is 2x - y - 7 = 3yi + xi
I'm confused as to what I should equate.
Reply 7
Original post by Erotas
Misread the y as a 1 :tongue: so the expansion is 2x - y - 7 = 3yi + xi
I'm confused as to what I should equate.


The real part = 0 and the imaginary part = 0.
Reply 8
Original post by tory88
1. Expand out the brackets and you'll get f(x,y) + g(x,y)i = 0. 0 is the same as 0+0i, so you can set f=0 and g=0 and solve as simultaneous equations.

2. If you look carefully this is just a quadratic, if you use the substitution x = a^2 then this should become something you're used to. Just remember to put a^2 back in at the end (or before solving will be easier in this case).

Any questions, quote me and I'll answer them.



The real part = 0 and the imaginary part = 0.


Thanks to both of you! :smile:
Reply 9
how do u know that?
Reply 10
how do u know that?


Please don't resurrect 10 year old threads! Most - if not all - of the people involved in the original discussion are probably no longer active here :smile:

If you have a specific question it's better to start your own new thread with any working that you have tried for the question, as per forum rules.