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# 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$$