Chapter 10 - Parametric Equations and Polar Coordinates - 10.3 Polar Coordinates - 10.3 - Page 707: 22

$$ \theta =\frac{\pi}{4}$$ or $$ \theta =\frac{5\pi}{4}$$

$$x=y$$ Here, $$x=rcosθ$$, and $$y=rsinθ$$ $$rcosθ=rsinθ$$ $$cosθ=sinθ$$ $$\frac{sin \theta}{cos \theta} =1$$ $$tan \theta =1$$ $$ \theta =\frac{\pi}{4}$$ or $$ \theta =\frac{5\pi}{4}$$