# Python acos: What is acos() Function in Python

Python math acos() function is used to find arc cosine. The math.acos() function takes a number between -1 to 1 and finds the arc cosine of that number.

The acos() is defined under the python math library. So, we have to import the math library before using it.

## Python acos

Python acos() is a built-in math function that returns the arc cosine of x in radians. The math.acos() method accepts the only number between the range of -1 to 1; if we provide a number out of the range, it returns a ValueError – “ValueError: math domain error”, and if we provide anything else except the number, it returns error TypeError – “TypeError: a float is required”.

### Syntax

`math.acos(number)`

The acos() function takes only one argument, and the number ranges from -1 to 1.

### Return Value

The acos() function returns the arc cosine of the given number.

If the given number is out of range (out of -1 to 1), it returns a ValueError. Also, if we pass anything except a number, it throws a TypeError.

### Programming Example

See the following code.

```# Importing math library
import math

# Taking input from user
n = int(input("Please enter number to find arc cosine: "))

# Finding cosine
print("Cosine of ", n, " is: ", math.acos(n))

# Initializing number out of range
n = 3
print("Cosine of ", n, " is: ", math.acos(n))
```

#### Output

```Please enter number to find arc cosine: 1
Cosine of  1  is:  0.0
Traceback (most recent call last):
File "acos1.py", line 12, in <module>
print("Cosine of ",n," is: ",math.acos(n))
ValueError: math domain error

```

In this program, we have taken input 1 from the user and called acos() function, and we got the output cosine of 1.
On the other hand, in the next line, we have initialized the value of n as 3, which is out of range, and we got one ValueError.

### Example 2

See the following code.

```# Importing math library
import math

# Initializing value which is not a number
n = '100'
# Finding cosine
print("Cosine of ", n, " is: ", math.acos(n))
```

#### Output

```Traceback (most recent call last):
File "acos2.py", line 7, in <module>
print("Cosine of ",n," is: ",math.acos(n))
TypeError: must be real number, not str
```

In this program, we have declared the value of n a string, which is not a number. As said earlier, we got TypeError.

## Conclusion

The Python acos Function allows you to find the trigonometry Arc Cosine for the numeric values. Python acos or Arc cosine, also called the inverse of a cosine.