# Integration

Integration 积分

## The meaning of $$\int$$

$$\int$$ is kind of like $$S$$ in $$sum$$.

$$\int_1^4 x$$ is different than $$\sum_{n=1}^{4} n$$.

In $$\sum_{n=1}^{4} n$$, n can only be increased by 1. So it will be $$1 + 2 + 3 + 4$$.

But in $$\int_1^4 x$$, $$x$$ can be any number in interval $$[1, 4]$$, $$dx$$ is another conception that not related in this $$x$$. So it will be $$1 + ... + 2 + ... + 3 + ... + 4$$

