im a fucking retard though. it says gradient of f is 3... no no it is not
edit: yes it is. if x =rcos(theta) and y=rsin(theta) then r is the radius and in the funtion x^2 + y^2 =9 the radius must be 3.
so, that being said
sqrt(x^2+ y^2) must be
sqrt(r^2) which is just r.
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