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# C1 Simultaneous Equations watch

1. Solve the simultaneous equations:

x-3y+7=0
x^2+2xy-y^2=0

I have substituted the first (rearranged into x=3y-7) into the second and I end up with:

14y^2-56y+49=0

which then simplifies to

2y^2-8y+7=0

and then I get stuck from there.

Have I made an error further up? The quadratic formula doesn't make it any nicer in regards to a solution to y, I think I ended up with 2±√2, which I don't think is correct.

Thanks for any help.
2. Looks correct to me
3. It looks fine; try calculating out y and then sub both of them back into each equation to check it.
4. It seems alright, except I get rather than what you have.
5. (Original post by nuodai)
It seems alright, except I get rather than what you have.
Yes sorry I got that just didn't concentrate while typing, it seems this is the right answer, it just didn't look nice at the end of loads of workings, thanks very much for the help everyone though.
6. Can you help me do :
x+y=2
x^2+2y=12
7. (Original post by cashmoneyorg)
Can you help me do :
x+y=2
x^2+2y=12
hey,

rearrange x+y = 2, to y = 2-x

then on the second equation put the 12 on the other sideto get
x^2+2y-12 = 0,

now can you see what to do?
8. (Original post by Extricated)
hey,

rearrange x+y = 2, to y = 2-x

then on the second equation put the 12 on the other sideto get
x^2+2y-12 = 0,

now can you see what to do?
nope
9. (Original post by cashmoneyorg)
nope
substitute your new y value into your second equation, you should get a quadratic, which you can solve.
10. (Original post by Extricated)
substitute your new y value into your second equation, you should get a quadratic, which you can solve.
maths is beautiful

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