Write the equation of each conic described below.

1. A circle centered at $(5, 1)$ with a circumference of $40π$.

   Hint (a):

   If the circumference of a circle is $2πr$, what is the radius of this circle?

2. An ellipse that has foci at $(3, 0)$ and $(−3, 0)$ and a major axis of length $10$.

   Hint (b):

   The center of the ellipse lies at the midpoint of the two foci.