# 2019_Question1_e

Note that x=y satisfies the equation, and so we have at least one straight line in the graph. But both \sin and \cos are 2\pi-periodic, so, in particular, f(x,y)=f(x+2\pi,y). This means that there are infinitely many straight lines, such as all those of the form y=x+2n\pi for n\in\mathbb{Z}.

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