# Thread: find the volume of the curves rotated about the x-axis

1. ## find the volume of the curves rotated about the x-axis

the endpoint comes -1 and 1

and I am taking the integral of ((9/8)-x^2)-(x^2/8)....and then multiplyig by 2pi.

the final answers come 3pi.

Any help

thanks

2. method of washers ...

$\displaystyle V = \pi \int_a^b [R(x)]^2 - [r(x)]^2 \, dx$

3. Originally Posted by skeeter
method of washers ...

$\displaystyle V = \pi \int_a^b [R(x)]^2 - [r(x)]^2 \, dx$
so its like this with end points of -1 and 1

4. Originally Posted by racewithferrari
so its like this with end points of -1 and 1
second term in the integrand should be $\left(\frac{x^2}{8}\right)^2$ if what you posted originally is correct ...

$\frac{x^2}{8} \ne \frac{1}{8x^2}$

also ... limits of integration?