Past exam of the mathematics course of the University of Cambridge / 2022 / ia / Paper 1 / 1B / a / iii / Solution

By the focal definition of an ellipse, the solution set is the ellipse with foci $a$ and $b$. Its centre is $(a+b)/2$, its major axis lies along the line through the foci, and its semiaxes areThe sketch is consequently a nondegenerate ellipse symmetric about both the focal line and its perpendicular bisector.