PreCalculus

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I'm so confused... I've always been good at math but this year I'm just not getting it. But I know i can I always get help and a REAL explanation from the people on here so...

A steel drum in the shape of a right circular cylinder required to have a volume of 100 cubic feet.
(a) Express the amount A of material required to the make the drum as a function of the radius "r" to the cylinder.
(b) How much material is required if the drum is of radius 3 feet?
(c) Of radius 4 feet?
(d) Of radius 5 feet?

I'm so confused, I don't even know where to start!!!

  • PreCalculus -

    They want the surface area of the cylinder, including top and bottom. The two ends have a combined area of 2 pi r^2. The side wall area is 2 pi r L, where L is the length. The relationship between L and r is
    pi r^2 L = 100

    Write the equation for A, using
    L = 100/(pi r^2) to eliminate L

    Then plug in the numbers.

  • PreCalculus -

    Thanks! I didn't realize it could be so easy!

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