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# What is function?

When we talk about function, it's typically a series of instruction which in a box and when you put variables in, it will return some certain result.

For example:

```
def add(a, b):
    return a + b
```

It's the same thing as $$f(a, b) = a + b$$ , which get variables `a` and `b` and return `a + b`.

But in math, we call the `a + b` y.

毫不夸张地说，老师一直以来都欺骗了我们，把它变得非常神秘。 事实上，函数就是 a function. A function 就是一系列“代码”用来实现一个特定的任务。（比如计算平方、计算数的变化）


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