- (D) See the figure. Since the area, A, of the ring equals π (y 22 − y 12 ),
A = π [(6x − x^2 )^2 − x^4 ] = π [36x^2 − 12x^3 + x^4 − x^4 ]
and = π (72x − 36x^2 ) = 36πx (2 − x).
It can be verified that x = 2 produces the maximum area.
dmanu
(dmanu)
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