Find the Value of (1/h²)+(1/r²) :

The numerical value of the volume and the area of the lateral surface of a right circular cone are equal If the height of the cone be h and radius be r, the value of (1/h²)+(1/r²) is

  1. 3/1
  2. 1/3
  3. 1/9
  4. 9/1
Anurag Mishra Professor Asked on 26th October 2015 in Maths.
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1 Answer(s)

Answer is (3): 1/9

Explanation:-
According to the question,
pai r2h/3 = pai r (h2 + r2)1/2
 r h/3 = (h2 + r2)1/2

Square on both side,
r2h2/9 = h2 + r2
1/9 = (h2 + r2)/r2h2
1/ 9 = h2/r2h2 + r2/h2r2
1/9 = 1/r2 + 1/h2

Then, the value of (1/r2) + (1/h2) is 1/9

Hence, the answer is (3) 1/9.

Monis Rasool Professor Answered on 28th October 2015.
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