First, it helps to know the limits of your integration. In this case, these will be where your graph intersects the axes...

intercept:

.

So is the intercept.

intercept:

.

So is the intercept.

Since you are rotating around the axis, it will be a integral, so your bounds are . Also note that if then

Now to set up the integral. This solid of revolution can be considered as the area rotated around the axis. This area needs to be thought of as a series of rectangles. Their length is the same as the value of , and their width is a small change in , which we call .

When you rotate the rectangles, they form cylinders. The radius of each cylinder is the same as the length of the corresponding rectangle, so the circular cross-sectional area of each cylinder is , and the height of each cylinder is the same as the width of each rectangle.

So the volume of each cylinder is and the total volume can be approximated by

.

As you increase the number of cylinders, the sum converges on an integral and the approximation becomes exact. So the volume is

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