e \; = \;  \frac{ c }{a } 

e_1 \; = \;  \frac{ c }{a_1 } 

e_2 \; = \;  \frac{ c }{a_2 } 

O_1 = Intersect(yAxis, xAxis)
a = 5.9 (slider from 0 to 15, step 0.1)
O = Intersect(yAxis, xAxis)
c = 2.9 (slider from 1 to 5, step 0.1)
b: sqrt(a * a - c * c)
F_1: (-(c), 0.0)
F_2: (c, 0.0)
e: x * x / (a * a) + y * y / (b * b) = 1.0
a_1 = 5.1 (slider from 0 to 15, step 0.1)
a_2 = 3.7 (slider from 0 to 15, step 0.1)
b_1: sqrt(a_1 * a_1 - c * c)
e_1: x * x / (a_1 * a_1) + y * y / (b_1 * b_1) = 1.0
b_2: sqrt(a_2 * a_2 - c * c)
e_2: x * x / (a_2 * a_2) + y * y / (b_2 * b_2) = 1.0