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I am running into trouble with this question:

I get as far as

$$1 = \cos y\frac{dy}{dx} - \sin y\frac{dy}{dx}$$

$$1 = \frac{dy}{dx} (\cos y - \sin y)$$

$$\frac{dy}{dx} = \frac{1}{\cos y-\sin y}$$

Second derivative:

Unsure how to continue here

3 Answers 3