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## Homework Statement

u^n (x,y)=nu^(n-1) (x,y) u' (x,y)

## Homework Equations

## The Attempt at a Solution

can i set f (x,y)=u^n (x,y)

lnf =lnu^n

lnf=nlnU

f'/f=n/U

f'=fn/U -(U(^n) )(n/U)

after that i dont know how to continue and is there a better way to prove it