The #key# **`ACOS()` function**:  also called the `arc cosine` function #key# returns the inverse cosine of a number. To be more specific, it returns the inverse cosine of a number in the radian float value. 

Figure 1 shows the mathematical representation of the `ACOS()` function and Figure 2 shows the visual representation of the `ACOS()` function.

# Syntax
```sql
ACOS(number)
```
# Parameter
This function requires a number as a parameter. The parameter must be a float value between -1 and 1, i.e., `-1 <= parameter <= 1`. 

# Return Value
`ACOS()` returns the `inverse cosine` of a number (radian float value) that is sent as a parameter. If the parameter is not between -1 and 1, it returns `NULL`.

# Example


/*example showing how to use ACOS(X)*/

-- positive number
select ACOS(1);

-- negative number
select ACOS(-1);

-- fractional number
select ACOS(0.6);

-- not between -1 and 1
select ACOS(3);
select ACOS(-3);


What is ACOS() in SQL?

Returns the inverse cosine of a number in radians; parameter must be between -1 and 1.