Solving a system of non-linear equations  TOPIC_SOLVED

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Solving a system of non-linear equations

Postby Luke53 on Tue Apr 19, 2011 1:42 pm

Hello, I need help on this one, tried out about everything, but still no use, can't solve the following system:
y² - x y - 4x = 0
x² - x y + 4 y - 12 = 0
I can't isolate x or y in either of the two equations for substituting in the other.
So what's the trick to solve this?

Luke.
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Re: Solving a system of non-linear equations  TOPIC_SOLVED

Postby nona.m.nona on Tue Apr 19, 2011 7:15 pm

Luke53 wrote:y² - x y - 4x = 0
x² - x y + 4 y - 12 = 0

One method might be to solve the first equation for Substitute the result into the second equation. Multiply through to clear the denominators, and expand.

Quite a few terms will drop out, leaving you with a quadratic which solves nicely with the Quadratic Formula.
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Re: Solving a system of non-linear equations

Postby Luke53 on Tue Apr 19, 2011 8:19 pm

y² - x y - 4x = 0
x² - x y + 4 y - 12 = 0
x=y²/(y+4) (didn't see that I could factor x out in the first eqn.)
Substituting this in the second eqn and solving gives: 20y²-32y-192=0
y=4 and y= -12/5
subst. y=4 into the system gives x=2
Thanks.
Luke.
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Posts: 54
Joined: Sun Mar 13, 2011 9:46 am


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