**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.