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## Homework Statement

Let f(x,y) be a differentiable function with x = rcosθ and y = rsinθ. find the df(x,y)^2/d^2θ (second derivative with respect the theta)

## Homework Equations

## The Attempt at a Solution

Don't exactly know what i'm doing here.. The notes from class give me this equation (btw f_xx will mean the second derivative with respect to x etc)

f_r = f_xcosθ + f_ysinθ

f_rr = f_xxcos^2θ + 2f_xycosθsinθ + f_yysin^2θ

f_xx + f_yy = f_rr + f_r / r + f_θθ / r^2

So i'm assuming I have to make use of these or something... Anyone wanna help me get started here?