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Solving 2 equation with 2 variables (hard)

  • Thread starter Zetison
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  • #1
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[PLAIN]http://folk.ntnu.no/jonvegar/images/math.gif [Broken]

I really need some help here (no program is allowed :smile:)
 
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Answers and Replies

  • #2
Pengwuino
Gold Member
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What work have you done on the problem so far?
 
  • #3
HallsofIvy
Science Advisor
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I'm not sure why you would consider that "hard". You can solve the second equation for x as a quadratic function of y. Putting that into the first equation gives a cubic equation for y.
 
  • #4
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The problem is to find exact values, not estimatet values. Therefore: do not use any programs...
 
  • #5
Gib Z
Homework Helper
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Indeed. Do you have any strategies to find a root? There are many you can try. Once you find one, you can divide and just solve a quadratic.
 
  • #6
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Here is what I have done so far:

[PLAIN]http://folk.ntnu.no/jonvegar/images/1.gif [Broken]
[PLAIN]http://folk.ntnu.no/jonvegar/images/2.gif [Broken]
[PLAIN]http://folk.ntnu.no/jonvegar/images/3.gif [Broken]
[PLAIN]http://folk.ntnu.no/jonvegar/images/4.gif [Broken]
[PLAIN]http://folk.ntnu.no/jonvegar/images/5.gif [Broken]
[PLAIN]http://folk.ntnu.no/jonvegar/images/6.gif [Broken]

But these solutions contains "cos". It is possible to rewrite the equations to the formula
[PLAIN]http://folk.ntnu.no/jonvegar/images/8.gif [Broken]
and then find solutions without any trigonometrical components.

That is my problem...
 
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  • #7
Gib Z
Homework Helper
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Would have been a simpler computation for the program to have changed the x into 1/y rather than the other way around, small numbers to deal with overall. Were you expected to solve this cubic analytically and it's roots actually looked like that?
 
  • #8
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Yes. It does not matter how you start. You will get the same solutions with the same trigonometrical components. Plz help me find solutions without any trigonometrical components.
 
  • #9
1,838
7
There is a typo in the problem: "79" should be "78".
 
  • #10
Gib Z
Homework Helper
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Is it just because the answer drops our nicely if that is the case, or do you somehow know it as a fact :S ?
 
  • #11
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I just somehow know it is a fact :smile:
There is a typo in the problem: "79" should be "78".
Sorry mac, it is "79"
 
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