Dedicated to my grandson Fedor.
The parametric equations of a pumpkin surface with n ridges are given to be:
X ( p , t , n ) Y ( p , t , n ) Z ( p , t , n ) = = = R sin ( p ) n ( n + 1 ) cos ( t ) − cos ( t ( n + 1 ) ) R sin ( p ) n ( n + 1 ) sin ( t ) − sin ( t ( n + 1 ) ) h cos ( p ) , where 0 ≤ t ≤ 2 π and 0 ≤ p ≤ π .
Define V p ( R , h , n ) as the pumpkin's volume, and V s ( R ) = 3 4 π R 3 .
If the value of V s ( R ) V p ( R , R , 1 2 ) can be expressed as B A , where A and B are coprime positive integers, submit your answer as A + B .
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@Mark Hennings , we really liked your comment, and have converted it into a solution.
What does n represent here?
Where can I find more information about the elementary volume element ratio?
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A better name for it is the Jacobian ∂ ( r , p , t ) ∂ ( x , y , z )
I guess I need to review calculus.
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With R = h we have the parametrization r = ( r sin p n ( n + 1 ) cos t − cos ( ( n + 1 ) t ) , r sin p n ( n + 1 ) sin t − sin ( ( n + 1 ) t ) , r cos p ) and hence we have the elementary volume element ratio X ( r , p , t ) = ∣ ∣ ∣ ∣ ∂ r ∂ r ⋅ ( ∂ p ∂ r × ∂ t ∂ r ) ∣ ∣ ∣ ∣ = n 2 2 ( n + 1 ) ( n + 2 ) r 2 sin p sin 2 2 1 n t so the pumpkin volume is V p ( R , R , n ) = ∫ 0 R d r ∫ 0 π d p ∫ 0 2 π d t X ( r , p , t ) = 3 n 2 4 ( n + 1 ) ( n + 2 ) π R 3 so that V s ( R ) V p ( R , R , n ) = n 2 ( n + 1 ) ( n + 2 ) This makes the correct answer 1 4 4 1 3 × 1 4 = 7 2 9 1 , so the desired answer is 1 6 3 .