5 Best Ways to get the Trigonometric Inverse Sine in Python

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πŸ’‘ Problem Formulation: In the realm of mathematics, the inverse sine function, also known as arcsin, is used to find the angle whose sine is a given number. In Python, obtaining this trigonometric inverse requires specific methods or libraries. Suppose you have a sine value of 0.5; you aim to determine the angle in radians corresponding to that sine value. This article explores multiple ways to calculate this in Python.

Method 1: Using math.asin

The math module in Python provides access to the mathematical function asin(), which returns the arc sine of a number in radians. The input number must be in the range [-1.0, 1.0], and it throws a ValueError if the input is outside this range.

Here’s an example:

import math
angle_rad = math.asin(0.5)

Output: 0.5235987755982989

The code snippet uses the asin() function from the math module to calculate the inverse sine of 0.5, which it then prints out as the angle in radians.

Method 2: Using numpy.arcsin

NumPy is a library that provides support for large, multi-dimensional arrays and matrices, along with a collection of mathematical functions to operate on these arrays. The numpy.arcsin() function is used to calculate the trigonometric inverse sine of each element in an input array.

Here’s an example:

import numpy as np
angle_rad = np.arcsin(0.5)

Output: 0.5235987755982989

This code demonstrates usage of NumPy’s arcsin() function to compute the inverse sine of 0.5, yielding the angle in radians. It’s especially useful for performing the operation on arrays of values.

Method 3: Using scipy.arcsin

The SciPy library builds on NumPy and provides additional functionality. SciPy’s arcsin() function is similar to NumPy’s but is sometimes preferred for scientific computations when used in conjunction with other SciPy functions.

Here’s an example:

from scipy import arcsin
angle_rad = arcsin(0.5)

Output: 0.5235987755982989

This example shows how to utilize SciPy’s arcsin() function for finding the inverse sine of 0.5. It’s particularly suitable when used in scientific computing contexts with SciPy’s broader ecosystem.

Method 4: Using sympy.asin

Symbolic computation deals with the computation of mathematical objects symbolically. SymPy, a Python library for symbolic mathematics, includes the asin() function. This method allows for computing the exact symbolic expression of the inverse sine.

Here’s an example:

from sympy import asin, rad
angle_rad = asin(0.5)

Output: pi/6

In this snippet, the asin() function from SymPy is employed to determine the symbolically exact angle whose sine is 0.5, and then the angle is converted to radians using the rad() function.

Bonus One-Liner Method 5: Using mpmath.asin

For high-precision arithmetic, the mpmath library is often the go-to choice. It provides its own version of the asin() function, which can be used similarly to those in other libraries, but with the ability to specify higher precision.

Here’s an example:

from mpmath import asin, mp
mp.dps = 15  # set decimal places to 15
angle_rad = asin(0.5)

Output: 0.523598775598299

This code utilizes the mpmath library’s asin() function, adjusting the decimal places for precision, to calculate the inverse sine of 0.5, resulting in a high-precision angle in radians.


  • Method 1: math.asin. Easy to use. Only for single float values. Situated in the standard library.
  • Method 2: numpy.arcsin. Ideal for array computations. Requires NumPy library. Offers high performance for large datasets.
  • Method 3: scipy.arcsin. Similar to NumPy. Best suited for scientific tasks within the SciPy ecosystem.
  • Method 4: sympy.asin. Provides exact symbolic results. Useful for theoretical computations. Requires SymPy library.
  • Method 5: mpmath.asin. Enables high-precision calculations. Good for applications requiring great numerical accuracy. Requires mpmath library.