Question

Find the volume of the solid generated by revolving the region enclosed by the triangle with vertices (1 comma 0 )​, (3 comma 2 )​, and (1 comma 2 )about the​ y-axis. Use the washer method to set up the integral that gives the volume of the solid.

Answer 1

Answer: Volume = $\frac{20\pi }{3}$

Step-by-step explanation: The washer method is a method to determine volume of a solid formed by revolving a region created by any 2 functions about an axis. The general formula for the method will be

V = $\pi \int\limits^a_b {(R(x))^{2} - (r(x))^{2}} \, dx$

For this case, the region generated by the conditions proposed above is shown in the attachment.

Because it is revolting around the y-axis, the formula will be:

$V=\pi \int\limits^a_b {(R(y))^{2} - (r(y))^{2}} \, dy$

Since it is given points, first find the function for points (3,2) and (1,0):

m = $\frac{2-0}{3-1}$ = 1

$y-y_{0} = m(x-x_{0})$

y - 0 = 1(x-1)

y = x - 1

As it is rotating around y:

x = y + 1

This is R(y).

r(y) = 1, the lower limit of the region.

The volume will be calculated as:

$V = \pi \int\limits^2_0 {[(y+1)^{2} - 1^{2}]} \, dy$

$V = \pi \int\limits^2_0 {y^{2}+2y+1 - 1} \, dy$

$V=\pi \int\limits^2_0 {y^{2}+2y} \, dy$

$V=\pi(\frac{y^{3}}{3}+y^{2} )$

$V=\pi (\frac{2^{3}}{3}+2^{2} - 0)$

$V=\frac{20\pi }{3}$

The volume of the region bounded by the points is $\frac{20\pi }{3}$.