need help plz... conic question (1 Viewer)

[victorheaven]

P is any point on the ellipse x^2/a^2+y^2/b^2=1, with foci S and S' , prove that PS+PS'=2a..
i thought this was what we define an ellipse. - -
can anyone help plz?

 

[ssglain]

Hint: Use the locus definition to write PS+PS' as ePM+ePM'.