How do you solve these kind of two variable function questions?

• Sep 14th 2009, 10:15 AM
Allan89a
How do you solve these kind of two variable function questions?
f(x,y) = x^2 + x(y^2 - 1)

and definition limit x^2 + y^2 = or < 17?

I know you use partial derivates to get the extreme points of f(x,y), but I don't understand how to solve for the extreme points on the definition limit circel. Someone could explain maybe, thanks?
• Sep 14th 2009, 03:04 PM
TKHunny
Have you met Lagrange Multipliers? That's one way.

You could go to the trouble to substitute and work the problem in one variable, but that might be a bit messy.
• Sep 15th 2009, 11:13 AM
Allan89a
No, I'm trying to do the substitution method.
• Sep 15th 2009, 02:19 PM
TKHunny
Fine. Substituting for y^2 actually looks pretty straight-forward. Let's see what you get.

Note: The direct substitution deal only with the EQUALITY of the expression. You must then think about the interior. Are there extrema on the inside of the structure? How can you tell?