Thread: torus

Hi , I'm having trouble with this problem:

Recall the formula for the volume of a torus (doughnut) with circular cross–section of radius

a rotated about a vertical axis a
distance b > a from its centre is 2pi(squared)a(squared)b. Suppose a + b = 3 in, inches say, what value

of a will maximise the volume of the torus?

Help!

Originally Posted by dannyshox

Hi , I'm having trouble with this problem:

Recall the formula for the volume of a torus (doughnut) with circular cross–section of radius

a rotated about a vertical axis a
distance b > a from its centre is 2pi(squared)a(squared)b. Suppose a + b = 3 in, inches say, what value

of a will maximise the volume of the torus?

Help!

Just substotute a=3-b in the expression of volume, then different it (with respect to b) to get the value of b for which volume is maximum.