Show that of all the rectangles inscribed in a given fixed circle, the square has the maximumarea.

Let the length of a rectangle be l and breadth be b and the radius of a circle is a and the diagonal’s length be 2a.
As per Pythagoras theorem,
(Hypotenuse)2 = (Perpendicular)2 + (Side)2
(2a)2= l2 + b2
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Area of rectangle = ![]()
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= ![]()



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4a2 = 2l2
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Using second derivative test,
l = ![]()
Then the area of rectangle is the maximum.
Since,
l = b =
, the rectangle is a square.
Hence proved.
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