Question: Write a parameterization for the curves in the xy-plane.
1. The line through the points (2, -1) and (1, 3).
2. A vertical line through the point (-2, -3).
3. An ellipse centered at the origin, crossing the x-axis at ±3 and the y-axis at ±7. Start at the point (-3, 0) and trace out the ellipse counterclockwise.