1.

Find the range of eccentricity of the ellipse `x^2/a^2+y^2/b^2=1`, (where a > b) such that the line segment joining the foci does not subtend a right angle at any point on the ellipse.

Answer» we know `x^2y^2=a^2e^2`
we need to prove
b>ae
`b^2>a^2e^2`
`b^2>a^2-b^2`
`2b^2>a^2`
`b^2/a^2>1/2`
`0`ein(0,1/sqrt2)`


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