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# Math.PI

Besides functions

`Math`

offers some mathematical constants.
`Math.PI`

gives π (roughly 3.14) and `Math.E`

gives Euler's number e (roughly 2.71).## Exercise

Write a function

Example:

`area`

that calculates the area of a circle.
The function is given the radius of the circle.Example:

`area(1)`

should return `π`

and `area(2)`

should return `4 * π`

.
+ Hint

```
function area(r) {
return Math.PI ... ;
}
```

+ Solution

```
function area(r) {
return Math.PI * r * r;
}
```