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CAF123
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Homework Statement
Given that [tex] f(x,y) = g(r,\theta), [/tex] where [itex] x = r\cos\theta [/itex] and [itex] y = r\sin\theta, [/itex] find formulae for [itex] \frac{∂f}{∂x} [/itex] and [itex] \frac{∂f}{∂y} [/itex] expressed entirely in terms of [itex] r, \theta, \frac{∂g}{∂r} , \frac{∂g}{∂\theta} [/itex].
The Attempt at a Solution
I said [tex] \frac{∂f}{∂x} = \frac{∂g}{∂x} = \frac{∂g}{∂r}\frac{∂r}{∂x} + \frac{∂g}{∂\theta}\frac{∂\theta}{∂x}. [/tex]
Rearranging x = rcos(θ) to r = x/(cos(θ) gave [itex] \frac{∂r}{∂x} = \sec\theta [/itex] and [itex] \frac{∂\theta}{∂x} = -\frac{1}{r\sin\theta} [/itex]
Can someone tell me if this is correct?
I used a similar method for [itex] \frac{∂f}{∂y} = \frac{∂g}{∂y} [/itex]
Many thanks