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# Simultaneous equations... watch

1. Hi,

I've been revising simultaneous equations for an up coming exam and for the most part had no problems, except for 2 examples (out of 40), which I just can't solve and can't figure out why/where I'm going wrong! The sheet only gives the final answers, with no solution. If anyone could show me the solution to these it'd be massively appreciated.

First one:

Second one:

These aren't any different to the others which I've done, which is why I'm so baffled as to why I can't solve them (it's the subsitution method I've been using). Again I'd greatly appreciate any help. Thanks.
2. For your first equation, substitute y = x + 6 into the quadratic one, and you get x^2 + (x+6)^2 = 50. Solve for x, then plug it into the above equation to solve for y. (If you draw the line y = x + 6 and the circle x^2 + y^2 = 50, you'll see you get two answers at the points of intersection.) For the second one, substitute y = 2x - 2 to get x^2 - (2x - 2) = 5, and do the same.

If you're still stuck, post your working.
3. I'll do the first one for you, than see if you can do the second one yourself.

4. for the first one, y^2 = (x+6)^2 ...work that out and plug it into the bottom equation

for the second one, x^2 -(2x - 2) = 5
5. Now remember to solve for y, and note which x solution goes with which y solution...
6. What are the answers? I get x=1, y=7 and x=-7 and y=-1 for the first and x=3, y=4 and x=-1 and y=-4 for the second. I don't want to start explaining how to get the wrong answers, though So, is these the answers you should get?
7. (Original post by samir12)
I'll do the first one for you, than see if you can do the second one yourself.

Ahhh! I was doing "x^2 + x^2 = x^4" not 2x^2. Thank you so much.

For the second I've been doing:
x^2 -(2x - 2) = 5
x^2 - 2x - 7 = 0

Then, of course, I'm stuck. Which makes me think I'm making yet another glaringly obvious and silly mistake.

Thanks for all the responses everyone, didn't expect so many so quick!

(Original post by miglash)
What are the answers? I get x=1, y=7 and x=-7 and y=-1 for the first and x=3, y=4 and x=-1 and y=-4 for the second. I don't want to start explaining how to get the wrong answers, though So, is these the answers you should get?
Yep, they're correct.

8. remember there is a -1 in front of the brackets, so -1 * -2 = + 2
9. (Original post by samir12)

remember there is a -1 in front of the brackets, so -1 * -2 = + 2
I knew it'd be something obvious like that. >.< Thanks. If my rep was worth any I'd give it.

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