Question -19

Calculus Level 3

Area of the greatest rectangle that can be inscribed in the ellipse x 2 a 2 + y 2 b 2 = 1 \dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}=1 is :


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a b ab a b \frac{a}{b} a b \sqrt{ab} 2 a b 2ab

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1 solution

Yash Sharma
Mar 14, 2015

imagine a circlular ring placed in xy plane .and hence the z-coordinate value of every point of this ring i is zero now rotate it through some angle such that the axis of rotation is the x axis...if you imagine the way i am trying to explain....you will find some points of the ring get positive z cordinate value some get negative z cordinate vaue.....and their y cordionate value also decreases..........now try to see this ring from the same position you were seeing it as before.............you will see an ELLIPSE.THAT IS THE XY PROJECTION OF THIS RING WILL NOW LOOK AS ELLIPLSE.........................rectangle with max. area on the circle ring was a square whose vertices have x cordinate value +or - ( a/sqrt2).............the same square will now appear as a rectangle with maximum area...............the x cordinates would still be same.hence we would be able to trace the length and breadth of the rectangle.........and hence area

circle

ellipse

THIS IS HOW I FEEL ELLIPSE..

didnt get wat u r saying(how come the projection appears as a ellipse) (-_-)?

prajwal kavad - 6 years, 2 months ago

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try to imagine...............................A CIRCLE DRAWN ON THE FLOOR and you are watching it it from a distance apart................you will see an ellipse...............................you will see it as a circle only and only if you watch it from a place directly above it .. .i have added something in the solution for you..............i know although the problem is simple and can be solved by different methods,,,,,,i just wanted to share a thought...........

Yash Sharma - 6 years, 2 months ago

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slove by maxima-minima method

Sanjoy Roy - 6 years ago

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