EllipseHard

Question

An ellipse has OB as semi minor axis, F and F′ its focii and the angle FBF′ is a right angle. Then the eccentricity of the ellipse is

Options

A.
B.
C.
D.

Solution

       
∵   ∠ FBF′ = 90o
∴   = (2ae)2
⇒   2(a2 e2 + b2) = 4a2e2
⇒   e2 = b2/a2
Also e2 = 1 - b2/a2 = 1 - e2
⇒   2e2 1, e =

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