Consider the parabola P:y2=4kx and the ellipse E:a2x2+b2y2=1. Let the line segment joining the points of intersection of P and E, be their latus rectums. If the eccentricity of E is e, then e2+22 is equal to ____.
Answer: 3
Solution
The common chord is a latus rectum of both curves: for y2=4kx it is x=k with ends (k,±2k), and for the ellipse it is x=ae with ends (ae,±b2/a). Matching the chords gives k=ae and 2k=ab2. Eliminating k, 2ae=ab2=a(1−e2), so e2+2e−1=0 and e=2−1. Then e2=3−22, and e2+22=3.