Answer
(a) $y=x$, (b) a line passing $(0,0)$, slope$=1$. See graph.
Work Step by Step
(a) Use the relations $r^2=x^2+y^2, r\ sin\theta=y, r\cos\theta=x, tan\theta=\frac{y}{x}$, we have $\theta=\frac{\pi}{4}\Longrightarrow tan\theta=\frac{y}{x}=tan\frac{\pi}{4}=1 \Longrightarrow y=x$
(b) We can identify the equation as a line passing $(0,0)$, slope$=1$ (rectangular system). See graph.
