Question

Write and evaluate the definite integral that represents the volume of the solid formed by revolving the region about the x-axis.
y= -x +4

Answer 1

Answer: V = $\frac{64}{3}\pi$

Step-by-step explanation: A solid formed by revolving the region about the x-axis can be considered to have a thin vertical strip with thickness Δx and height y = f(x). The strip creates a circular disk with volume:

V = $\pi. y^{2}.$Δx

Using the Disc Method, it is possible to calculate all the volume of these strips, giving the volume of the revolved solid:

V = $\int\limits^a_b {\pi. y^{2} } \, dx$

Then, for the region generated by  y = - x + 4:

V = $\int\limits^4_0 {\pi.(-x+4)^{2} } \, dx$

V = $\pi.\int\limits^4_0 {(x^{2}-8x+16)} \, dx$

V = $\pi.(\frac{x^{3}}{3}-4x^{2}+16x )$

V = $\pi.(\frac{4^{3}}{3}-4.4^{2}+16.4 - 0 )$

V = $\frac{64}{3}.\pi$

The volume of the revolved region is V = $\frac{64}{3}.\pi$