Prove that the area of a right angled triangle of given hypotenu

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 Multiple Choice QuestionsLong Answer Type

341. Prove that the volume of the largest cone that can be inscribed in a sphere of radius R is 8 over 27 of the volume of the sphere.
Or
Find the volume of the largest cone that can be inscribed in a sphere of radius r.

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 Multiple Choice QuestionsShort Answer Type

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345.

Show that the right circular cone of least curved surface and given volume has an altitude equal to an altitude equal to square root of 2 times the radius of the base.

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 Multiple Choice QuestionsLong Answer Type

346.

Find the altitude of a right circular cone of maximum curved surface which can be inscribed in a sphere of radius r.

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347.

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348.

Prove that the area of a right angled triangle of given hypotenuse is maximum when the triangle is isosceles.


Let ABC be right angled triangle in which
        angle ABC space equals space 90 degree
     AB space equals space straight x comma space space space space AC space equals space straight y
therefore space space space space space space space space BC space equals space square root of straight y squared minus straight x squared end root space where space straight y space is space hypotenuse.

Let ∆ denote the area of triangle ABC.
 therefore space space space space space increment space equals space 1 half BC. space AB space equals space 1 half square root of straight y squared minus straight x squared end root space space. straight x
space space space space fraction numerator straight d increment over denominator dx end fraction space equals space 1 half open square brackets straight x. space straight d over dx open parentheses square root of straight y squared minus straight x squared end root close parentheses space plus space square root of straight y squared minus straight x squared end root. space straight d over dx left parenthesis straight x right parenthesis close square brackets
space space space space space space space space space space space space space space space equals space 1 half open square brackets straight x. space fraction numerator negative 2 straight x over denominator 2 square root of straight y squared minus straight x squared end root end fraction plus square root of straight y squared minus straight x squared end root. space 1 close square brackets space space space space space space space left square bracket Here space straight y space is space constant right square bracket
space space space space space space space space space space space space space space space equals space 1 half open square brackets fraction numerator negative straight x squared plus straight y squared minus straight x squared over denominator square root of straight y squared minus straight x squared end root end fraction close square brackets space equals space 1 half open square brackets fraction numerator left parenthesis straight y squared minus 2 space straight x squared over denominator square root of straight y squared minus straight x squared end root end fraction close square brackets
Now space space space fraction numerator straight d increment over denominator dx end fraction space equals space 0 space space gives space us space space space space space 1 half open square brackets fraction numerator straight y squared minus 2 straight x squared over denominator square root of straight y squared minus straight x squared end root end fraction close square brackets space space equals 0 comma space space space space space space or space straight y squared space minus space 2 straight x squared space equals space equals 0
therefore space space space space space straight x squared space equals space space straight y squared over 2 space space space space space space space space space space space space space space rightwards double arrow space space space space space space straight x space equals plus-or-minus fraction numerator straight y over denominator square root of 2 end fraction.
Rejecting straight x space equals space minus fraction numerator straight y over denominator square root of 2 end fraction comma space space space we space get comma space space space space straight x space equals space fraction numerator straight y over denominator square root of 2 end fraction.
                 fraction numerator straight d squared increment over denominator dx squared end fraction space equals space 1 half open square brackets fraction numerator square root of straight y squared minus straight x squared end root. space left parenthesis negative 4 straight x right parenthesis space minus space left parenthesis straight y squared minus 2 straight x squared right parenthesis. space space begin display style fraction numerator negative 2 straight x over denominator 2 square root of straight y squared minus straight x squared end root end fraction end style over denominator straight y squared minus straight x squared end fraction close square brackets
space space space space space space space space space space space space space space equals space fraction numerator 1 over denominator space 2 end fraction open square brackets fraction numerator begin display style fraction numerator negative 4 straight x square root of straight y squared minus straight x squared end root over denominator 1 end fraction end style plus begin display style fraction numerator straight x left parenthesis straight y squared minus 2 straight x squared right parenthesis over denominator square root of straight y squared minus straight x squared end root end fraction end style over denominator straight y squared minus straight x squared end fraction close square brackets
space space space space space space space space space space space space space space space space equals space 1 half open square brackets fraction numerator negative 4 straight x left parenthesis straight y squared minus straight x squared right parenthesis space plus space straight x left parenthesis straight y squared minus 2 straight x squared right parenthesis over denominator left parenthesis straight y squared minus straight x squared right parenthesis to the power of begin display style 3 over 2 end style end exponent end fraction close square brackets space space space space space space space space space space space space space space space

                  equals space 1 half open square brackets fraction numerator negative 4 xy squared plus 4 straight x cubed plus xy squared minus 2 straight x cubed over denominator left parenthesis straight y squared minus straight x squared right parenthesis to the power of begin display style 3 over 2 end style end exponent end fraction close square brackets space equals space open square brackets fraction numerator 2 straight x cubed minus 3 xy squared over denominator left parenthesis straight y squared minus straight x squared right parenthesis to the power of begin display style 3 over 2 end style end exponent end fraction close square brackets
 When space straight x space equals space fraction numerator straight y over denominator square root of 2 end fraction comma space space space fraction numerator straight d squared increment over denominator dx squared end fraction space equals space 1 half open square brackets fraction numerator 2. space begin display style fraction numerator straight y cubed over denominator 2 square root of 2 end fraction end style space minus 3 space straight y squared. begin display style fraction numerator straight y over denominator square root of 2 end fraction end style over denominator open parentheses straight y squared minus begin display style straight y squared over 2 end style close parentheses to the power of begin display style 3 over 2 end style end exponent end fraction close square brackets
space space space space space space space space space space space space equals 1 half open square brackets fraction numerator begin display style fraction numerator straight y cubed over denominator square root of 2 end fraction end style minus begin display style fraction numerator 3 straight y cubed over denominator square root of 2 end fraction end style over denominator begin display style fraction numerator straight y cubed over denominator 2 square root of 2 end fraction end style end fraction close square brackets space equals space 1 half open square brackets fraction numerator negative square root of 2 space straight y cubed over denominator begin display style fraction numerator straight y cubed over denominator 2 square root of 2 end fraction end style end fraction close square brackets space equals space minus 2 space less than space 0
therefore space space space space increment space is space maximum space when space straight x space equals space fraction numerator straight y over denominator square root of 2 end fraction
therefore space space space space AB space equals space fraction numerator straight y over denominator square root of 2 end fraction
space space space space space space space space space space BC space equals space square root of straight y squared minus straight x squared end root space equals space square root of straight y squared minus straight y squared over 2 end root space equals space fraction numerator straight y over denominator square root of 2 end fraction
therefore space space space space AB space equals space BC space space space space space rightwards double arrow space space space space increment ABC space is space isosceles.

∴   area of a right-angled triangle of given hypotenuse is maximum when the triangle is isosceles.

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349. Prove that the perimeter of a right-angled triangle of given hypotenuse is maximum when the triangle is isosceles.
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350.

Prove that the perimeter of a right-angled triangle of given hypotenuse equal to 5 cm is maximum when the triangle is isosceles.

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