Hello! I have a math problem (mostly proofs) that im stuck(adsbygoogle = window.adsbygoogle || []).push({});

on, partially because I do not know where to begin and partially

because I believe I dont even fully understand the problem. I

was wondering if any of you would be kind enough to show me what to

do? Thank you.

1. Suppose f(x,y) is differentiable for all (x,y), f(x,y)=17 on the

unit circle x^2+y^2=1 and grad f is never zero on the unit circle. For

any real number K, find a unit vector parallel to grad

f(cos(k),sin(k))....grad f stands for the gradient of f. But isnt it contradicting what its saying? It says f(x,y)=17 on the unit circle x^2+y^2. How the...?

I'm just supposing f(x,y) is differentiable for all (x,y), f(x,y)=17 on the unit circle x^2+y^2=1 and grad(f) is never zero on the unit circle(?) So you just find a unit vector parallel to grad f(cos(k),sin(k)), for k real, right?

PS- Do level curves apply to this problem?

**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!

# Calculus problems, where to begin?

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