What are the absolute min and max of f(x,y)=xy^2 over a specific domain?

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Find the absolute min & absolute max of

f(x,y)=xy^2

with domain x^2+y^2\leq4

Please help
 
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Look for critical points on the interior x^2+y^2<4 and then check the boundary x^2+y^2=4. You should be able to at least get started.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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