In MySQL, the ACOS() function returns the arc cosine of a number.

You provide the number as an argument when calling the function.

Syntax

The syntax goes like this:

ACOS(X)

Where X is the value for which you’d like the arc cosine returned. The argument must be a value in the range -1 to 1. If it’s outside of that range, NULL is returned.

Example 1 – Basic Usage

Here’s a basic example.

SELECT ACOS(0.1);

Result:

+--------------------+
| ACOS(0.1)          |
+--------------------+
| 1.4706289056333368 |
+--------------------+

Here’s what happens when you provide a value of 1.

SELECT ACOS(1);

Result:

+---------+
| ACOS(1) |
+---------+
|       0 |
+---------+

And here’s what happens when you provide a value of -1.

SELECT ACOS(-1);

Result:

+-------------------+
| ACOS(-1)          |
+-------------------+
| 3.141592653589793 |
+-------------------+

Example 2 – Out-Of-Range Values

As mentioned, providing a value outside the range -1 to 1 returns a NULL value.

SELECT ACOS(2);

Result:

+---------+
| ACOS(2) |
+---------+
|    NULL |
+---------+

Example 3 – Expressions

You can also pass in expressions like this:

SELECT ACOS(0.1 + 0.3);

Result:

+--------------------+
| ACOS(0.1 + 0.3)    |
+--------------------+
| 1.1592794807274085 |
+--------------------+

Example 4 – Zero

Zero is within the accepted range.

SELECT ACOS(0);

Result:

+--------------------+
| ACOS(0)            |
+--------------------+
| 1.5707963267948966 |
+--------------------+

Example 5 – NULL

Passing in NULL returns NULL.

SELECT ACOS(NULL);

Result:

+------------+
| ACOS(NULL) |
+------------+
|       NULL |
+------------+

Return the Arc Sine

You can also return the arc sine of a value using the ASIN() function.