In the first question, x y=0 is substituted into the circular equation to solve the ellipse intersection points (0,-1)(4, 0) respectively.

According to the properties of ellipse, b= 1 a=4.

So the equation is x 2/16+y 2 =1.

The root number 3 of the second question c=2

Pf 1xpf2 = a 2-e 2x 2 is the focal radius, and the abscissa of formula x is p.

So when x=0, the maximum value of PF 1XPF2 is a 2 = 13.

Because C 2 = 12 and b= 1.

So the equation is x 2/13+y 2 =1.