Pi has been studied for thousands of years, and there are many different ways to calculate it. One of the most common methods is to use the Gregory-Leibniz series:
$$\pi = 4 \sum_{n=0}^{\infty} \frac{(-1)^n}{2n+1}$$
This series converges slowly, so it is not very useful for calculating pi to a high degree of accuracy. However, there are other methods that can be used to calculate pi much more quickly.
Pi has many important applications in mathematics and science. It is used in formulas for calculating the area and circumference of circles, the volume of spheres, and the surface area of other shapes. It is also used in physics, engineering, and other fields.
The number pi is a fascinating and important constant, and it continues to be studied by mathematicians and scientists today.