One (-4,3)
K 1=3/(c-4) K2=3/(-4-c)
AF 1 perpendicular to AF2.
K 1*K2 = - 1
c^2=25
F 1(-5,0) F2(5,0)
af 1 =√ 10 AF2 = 3√ 10
AF 1+AF2 = 4√ 10 =2a
a = 2√ 10
x^2/40 + y^2/ 15 = 1