Which of the equations below are equations
of a circular cylinder?
1. r (x, \theta) = \langle 3x, \sin 90, \sin 90\rangle
2. r (x, \theta) = \langle x, \cos 80, \sin 80\rangle
3. r (x, \theta) = \langle 5 \sin 70, x, 8 \cos 70\rangle
4. r (x, \theta) = \langle x, x \cos 30, x \sin 30\rangle
5. r (x, \theta) = \langle x \sin 70, x, x \cos 70\rangle