# Python – math.acos() function

• Last Updated : 28 May, 2020

Math module contains a number of functions which is used for mathematical operations. The math.acos() function returns the arc cosine value of a number. The value passed in this function should be in between -1 to 1.

Syntax: math.acos(x)

Parameter:This method accepts only single parameters.

• x :This parameter is the value to be passed to acos()

Returns:This function returns the arc cosine value of a number.

Below examples illustrate the use of above function:

Example 1:

 `# Python code to implement``# the acos()function``      ` `# importing "math"``# for mathematical operations  ``import` `math  ``     ` `a ``=` `math.pi ``/` `6``      ` `# returning the value of arc cosine of pi / 6  ``print` `(``"The value of arc cosine of pi / 6 is : "``, end ``=``"")  ``print` `(math.acos(a))`

Output:

```The value of arc cosine of pi / 6 is : 1.0197267436954502
```

Example 2:

 `# Python code implementation of ``# the acos() function``import` `math ``import` `numpy as np ``import` `matplotlib.pyplot as plt  ``   ` `in_array ``=` `np.linspace(``-``(``1` `/` `3.5` `*` `np.pi), ``1` `/` `3.5` `*` `np.pi, ``20``) ``   ` `out_array ``=` `[] ``   ` `for` `i ``in` `range``(``len``(in_array)): ``    ``out_array.append(math.acos(in_array[i])) ``    ``i ``+``=` `1``    ` `print``(``"Input_Array : \n"``, in_array)  ``print``(``"\nOutput_Array : \n"``, out_array)  `` ` ` ` `plt.plot(in_array, out_array, ``"go-"``)  ``plt.title(``"math.acos()"``)  ``plt.xlabel(``"X"``)  ``plt.ylabel(``"Y"``)  ``plt.show() `

Output:

```Input_Array :
[-0.8975979  -0.80311391 -0.70862992 -0.61414593 -0.51966194 -0.42517795
-0.33069396 -0.23620997 -0.14172598 -0.04724199  0.04724199  0.14172598
0.23620997  0.33069396  0.42517795  0.51966194  0.61414593  0.70862992
0.80311391  0.8975979 ]

Output_Array :
[2.6850860217724004, 2.50329950258761, 2.358350863035667, 2.2320996324218134,
2.1172515505585388, 2.009954812757658, 1.9078351422171613, 1.809259917693194,
1.7130011090538158, 1.6180559117526183, 1.5235367418371748, 1.4285915445359774,
1.3323327358965993, 1.233757511372632, 1.131637840832135, 1.0243411030312544,
0.9094930211679799, 0.783241790554126, 0.6382931510021833, 0.45650663181739287]
```

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