If two concentric ellipse be such that the foci of one be on the other and if and be their eccentricities. If be the angle between their axes, then the value of must be
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Let S and be the foci of one ellipse and H and be the other, C being their common centre. Then, is a parallelogram and since
Since the sum of the focal distance of any point on an ellipse is equal to its major axis which is 2a.
Then,
Let be the angle between their axes.
Then,
Now,
Squaring both sides, then
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