How do you use the method of cylindrical shells to find the volume of the solid obtained by rotating the region bounded by y = 1/x^4y=1x4, y = 0, x = 1, x = 4 revolved about the x=-4?

1 Answer
Dec 16, 2017

(57pi)/1657π16

Explanation:

the formula for the shell method is int_a^b2pirhdxba2πrhdx

aa and bb are the x-bounds, which are x=1 and x=4, so a=1a=1 and b=4b=4.

rr is the distance from a certain x-value in the interval [1,4][1,4] and the axis of rotation, which is x=-4. r=x-(-4)=x+4r=x(4)=x+4

hh is the height of the cylinder at a certain x-value in the interval [1,4][1,4], which is 1/x^4-0=1/x^41x40=1x4 (because 1/x^41x4 is always greater than 00 and h must be positive).

plugging it all in: volume =int_1^4(2pi(x+4)(1/x^4))dx=41(2π(x+4)(1x4))dx
you should get: (57pi)/1657π16