If α and β are the eccentric angles of the extremities of a focal chord of an ellipse, then the eccentricity of the ellipse is
Equation of chord function P(α) and Q(β) is
xacos α+β2 + ybsin α+β2 = cos α−β2
S(ae,0) is on their line
e cos α+β2+0 = cos α−β2
e = cos α−β2cos α+β2*sin α+β2sin α+β2*22 = sin α+sin βsin (α+β)