Lagrange multiplier method

  • Thread starter sara_87
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  • #1
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Question:

Use Lagrange multiplier method to determine the point on the curve
y=1-[tex]x^2[/tex]
that maximises the function f(x,y)=2x + y.
Hence find the maximum value of f.

Attempt at Solution:

Okay I used the Lagrange method to get a point on the curve and I got (1,0)

How do I find the maximum value of f though?
 

Answers and Replies

  • #2
cristo
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If you've found the values of x and y where the function has a maximum, then do you not just plug (1,0) into f(x,y) to obtain the value of the function at that point?
 
  • #3
Dick
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Uh, substitute (1,0) into f?
 
  • #4
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i get (0,0)?
 
  • #5
Dick
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f is a number. Not a point. And it's not 0.
 
  • #6
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i'm still stuck! i don't what to do lol
give me more tips before i give up on maths altogether!!
(does anyone else go through a phase when they just want to give up? lol)
 
  • #7
Dick
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You say f(x,y)=2*x+y. You've found a solution (1,0) so x=1, y=0. What is f(x,y)? Don't get so flustered!
 
  • #8
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'Don't get so flustered!'

you don't know what kind of day i've had! lol

thank you for your help and time i'm sure it's not a hard question i'll think about it tomorrow when i feel more awake.
 
  • #9
Dick
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Your annoyance is blocking you from seeing the obvious. That makes it a really good time to take a rest.
 

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