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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