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1 min read•june 8, 2020

Anusha Tekumulla

The **disc method **is a way to find the volume by **rotating around the x- or y-axis**. In this situation, we will find the volume by adding up a bunch of infinitely thin **circles**.

Let’s look at the region between the curve y = √x and the x-axis from x = 0 and x = 1.

If you **rotate this region** around the x-axis, the **cross sections will be circles with radii √x**. Thus, the area of each cross section will be π(√x)^2 or πx. Now we can **integrate **πx from x = 0 and x = 1 to get the volume.

Now, let’s generalize this. If you have a region whose area is bounded by the curve y = f(x) and the x-axis on the interval [a,b], each disk has a radius of f(x), and the area of the disk will be

**π[f(x)]2**

To find the volume, **evaluate the integral. **

Now, you try to use the formula with this example problem:

If rotate the function y = x + 2 about the x-axis from x = 0 to x = 2, what is the volume of the figure?

**Answer**: 58.643

**Solution**: In this example, your function is y = x + 2 which looks like this:

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