# acos in R: How to Use acos() Function in R

The arccos function is an inverse of the cos() function. It returns the angle whose cosine is a given number. Means: The angle whose cosine is 0.866 is 30 degrees. Use arccos or acos function when you know the cosine of an angle and want to know the actual angle.

## acos in R

The acos() is an inbuilt mathematical R function that returns the radian arccosine of number data. To calculate the arc cosine of the specified radian value, use the acos() function in R programming. The acos() function also returns the value in radians.

### Syntax

``acos(radian)``

### Parameters

The acos() function takes radian as an argument.

### Return Value

The acos() function returns the arc cosine value of radian. It is a Numeric value, array, or vector.

### Example

``acos(1)``

#### Output

`` 0``

## Passing a pi to the acos() function

The pi is an inbuilt constant in R programming, and its value is 3.141593.

Let’s find the pi constant’s acos() value.

``acos(pi)``

#### Output

`````` NaN
Warning message:
In acos(pi) : NaNs produced``````

You can see that it returns NaN(not a number) in the output.

Let’s see another example of pi.

``acos(pi / 4) ``

#### Output

`` 0.6674572``

## Applying an acos() function to Vector

To create a Vector in R, use the c() function. But, first, let’s create a vector and pass that to the acos() function.

``````data <- c(-1, -0.850250, -0.507107, -0.4, 0, 0.4, 0.507107, 0.850250, 1)
acos(data) ``````

#### Output

`````` 3.1415927 2.5872564 2.1026212 1.9823132 1.5707963 1.1592795 1.0389715
 0.5543363 0.0000000``````

That is it for this tutorial.