## How to calculate the area of a circle

If you cut the circles and stick them together, they gradually become more rectangular. In this rectangle, the width is half of the circumference, and the height is the radius.

Therefore, The area of a circle can be calculated as shown below.

## Integral: Split infinitely, and sum them all again

How can you find the area of the graph like the picture below?

Any shape can be split infinitely into a long stick shape. If you sum all the areas of these sticks together, you can find the original area.

Integral is possible even if it is not necessarily for calculating the area. For example, by accumulating an object's speed that changes over time with time, you can find out the distance the object has traveled.

Humankind has developed an integral method that can cope with a number of functions such as quadratic and cubic functions, multi-order functions, trigonometric functions, logarithms, and exp. For more information, please refer to the Mathematics Book.

In recent years, computers are often used to calculate integrals. Computers can calculate irregularly shaped integrals in a short time with little error.