Simultaneous Equation Help Please :)

[Guitarman0]

Hi there,

I have a simultaneous equation question that has been driving me crazy and I just can't see what I am doing wrong.

x^2 - 2y^2 = 8

x + 2y = 8

So, here is what I did:

I squared the 2nd equation to get

x^2 + 2y^2 = 64

I then added the new equation and the x^2 - 2y^2 = 8 equation to get

2x^2 = 72

I then divided both sides by 2 to get

x^2 = 36

and then square rooted x to get

x = 6

However, this doesn't work for both equations and the answers in the back of the book say x = 4, y = 2 OR x = -20, y = 14.

Could someone please show me where I am going wrong

Cheers

 

[Guitarman0]

Thanks for the replies guys, I got it sorted now. I tried the same method as you gave shayper earlier but made the mistake of thinking 2y x 2y = 2y^2 (noob mistake lol).

Thanks a lot