(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I really, really don't understand. My work shows one thing, and a simple look at the function shows another.

f(x,y) = .25x^2 + 5y^7 + 6y^2 - 3x

Find global max and min if they exist.

2. Relevant equations

3. The attempt at a solution

Took partial derivatives, solved each one for 0.

.5x - 3 = 0 => x = 6

35y^6 + 12y = 0 => y = 0

So a critical point is at (6,0), period.

Discriminant comes out to be

[.5][210y^5 + 12] - 0

Which comes out to be 6, since y = 0.

Therefore the discriminant is > 0, and the partial wrt x is > 0, so a global min occurs at (6,0). Period.

But wait! I submit this answer, and it basically says "nah, forget all that math crap. As y grows without bound, so does the function, so no global max or min."

???

Shouldn't the normal process lead me to that conclusion SOME HOW?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Global extrema, Calc III

**Physics Forums | Science Articles, Homework Help, Discussion**