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# AS Maths - Simultaneous Equations! watch

1. Hiya,

There's two simultaneous equations I just cannot seem to work out....help anyone?

1) xy = 15
y = 2x -1

2) y = 4x + 14
xy = 12

Thanks!
2. Well, what are you stuck on? Post your working. It should be basic substitutions.
3. substitute y in the first equation and you will get the value for X. then once u get the value for x substitute it in Y and you will get the value...

This is like gcse easy math...
4. for 1) sub eq2 in eq1
x(2x-1) = 15
multiply out brackets
2x^2 -x =15
collect on left
2x^2 - x -15 =0
factorise
(2x+5)(x-3)=0
so x =3 or 5/2

so try and do no. 2 from that subbing y into eq2.
5. 1)
xy = 15
y = 2x-1,
x(2x-1) = 15
2x^2-x-15=0
(2x+5)(x-3)=0
x = -5/2 or x = 3

2)
y=4x+14
xy=12
x(4x+14)=12
4x^2+14x-12=0
2x^2+7x-6=0
(2x-3)(x-2)=0
x=3/2 or x=2
6. (Original post by dotty_but_good)
for 1) sub eq2 in eq1
x(2x-1) = 15
multiply out brackets
2x^2 -x =15
collect on left
2x^2 - x -15 =0
factorise
(2x+5)(x-3)=0
so x =3 or 5/2

so try and do no. 2 from that subbing y into eq2.
Thanks a lot!
7. (Original post by IAmTheChosenOne)
1)
xy = 15
y = 2x-1,
x(2x-1) = 15
2x^2-x-15=0
(2x+5)(x-3)=0
x = -5/2 or x = 3

2)
y=4x+14
xy=12
x(4x+14)=12
4x^2+14x-12=0
2x^2+7x-6=0
(2x-3)(x-2)=0
x=3/2 or x=2
Thank-you!

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