Question
P is a point on the ellipse . The in-radius of ΔPSS’ (S and S’ are focii), where its area is maximum.
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- None of these
Hint:
find the dimensions of the triangle and find the values of semiperimetre and Area. use the formula r = A/ s to find the in radius.
The correct answer is:
let P be (a cos t, b sin t)
area of triangle PSS’ = ½ (2ae)(b sin t) = abe (sin t)
area is maximum when t= 90
hence, point P is (0,b)
area of triangle = abe
length of side PS = √a2e2+b2
semi perimeter = (2ae + 2√a2e2+b2)/2
= ae + √a2e2+b2
In radius = abe / (ae + √a2e2+b2)
= abe /( ae + a ) = be /(1+e)
in radius is the radius of the circle inscribed inside the triangle.
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