Solution
To convert from polar coordinate to rectangular coordinate,
[tex]\begin{gathered} (r,\theta)\to(r\cdot\cos \theta,r\cdot\sin \theta) \\ \\ \Rightarrow(3\sqrt[]{5},-\frac{\pi}{8})\to(3\sqrt[]{5}\cdot\cos (-\frac{\pi}{8}),3\sqrt[]{5}\cdot\sin (-\frac{\pi}{8})) \\ \\ \Rightarrow(3\sqrt[]{5}\cdot\cos (-\frac{\pi}{8}),3\sqrt[]{5}\cdot\sin (-\frac{\pi}{8}))=(6.20,-2.57) \end{gathered}[/tex]
