Problem 5.178

What kind of polarization has a plane electromagnetic wave if the projections of the vector $\mathbf{E}$ on the $x$ and $y$ axes are perpendicular to the propagation direction and are defined by the following equations: (a) $E_{x}=E \cos (\omega t-k z), E_{y}=E \sin (\omega t-k z)$ (b) $E_{x}=E \cos (\omega t-k z), E_{y}=E \cos (\omega t-k z+\pi / 4)$ (c) $E_{x}=E \cos (\omega t-k z), E_{y}=E \cos (\omega t-k z+\pi)$