+536 The problem is that you are trying to minimize the radius of a cone.. and this is the algebraic problem..
Good Luck
+128475 0 = pi ( r^2 + 900 / [ pi^2 * r^4] )^(1/2) + (pi *r / 2)( r^2 + 900 / [ pi^2 * r^4] )^(-1/2) *(2r - (3600) / [pi^2*r^5] )
- pi ( r^2 + 900 / [ pi^2 * r^4] )^(1/2) = (pi *r / 2)( r^2 + 900 / [ pi^2 * r^4] )^(-1/2) *(2r - (3600) / [pi^2*r^5] )
- ( r^2 + 900 / [ pi^2 * r^4] ) = ( r/2 ) (2r - (3600) / [pi^2*r^5] )
- ( r^6 * pi^2 + 900) / [ pi^2 * r^4 ] = (r/2) ( 2r^6 *pi^2 -3600) / [pi^2 * r^5 ]
- ( r^6 * pi^2 + 900)r = (r/2) ( 2r^6 * pi^2 - 3600)
- ( r^6 * pi^2 + 900)r = r ( r^6 * pi^2 - 1800)
- r^7*pi^2 - 900r = r^7 * pi^2 - 1800r
2r^7 * pi^2 - 900 r = 0
r ( r^6 * pi^2 - 450) = 0
r = 0 [ no good ] ..... or........
r^6 * pi^2 - 450 = 0
r^6 * pi^2 = 450
r^6 = 450 / pi^2
r^6 = [225 *2] / pi^2
r^6 = [2 * 15^2 ] / pi^2
r = 6√ 2 * 3√ (15 / pi) ≈ 1.8901
