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How to Find Cube Root in Python

The cube root means a number that produces a given number when cubed. The cube root of a number is a value that, when multiplied thrice or three times, produces the original value. 

The cube root symbol is denoted by ‘3√’. In the case of square root, we have used just the root symbol such as ‘√’, also called a radical.

For example, the cube root of 64, denoted as 3√64, is 4 because when we multiply 4 by itself three times, we get 4 x 4 x 4 = 64 = 43.

Cube Root in Python

To find the cube root in Python, use the simple math equation: x ** (1. / 3). It computes the (floating-point) cube root of x. It is a simple math equation takes the cube root of x, rounds it to the nearest integer, raises it to the third power, and checks whether the result equals x.

x = 27

cr = x ** (1./3.)

print(cr)

Output

3.0

To calculate the exponent number in Python, we use the **. The double star(**) is also called the power operator. To calculate the cube root, we can set the power equal to 1/3.

Find a cube root of a negative number in Python.

To find the cube root of a negative number in Python, first, use the abs() function, and then you can use the simple math equation to calculate the cube root.

We can not find the cube root of the negative numbers the way we calculated for the above method. For example, the cube root of integer -27 should be -3, but Python returns 1.5000000000000004+2.598076211353316j.

Let’s write a complete function that will check if the input number is negative, then it will calculate accordingly.

def cuberoot(x):
    if x < 0:
        x = abs(x)
        cube_root = x**(1/3)*(-1)
    else:
        cube_root = x**(1/3)
    return cube_root


print(cuberoot(27))
print(round(cuberoot(-27)))

Output

3.0
-3

As you can see, we need to round the result to get the cube root’s exact value.

Using Numpy cbrt() function

To find a cube root in numpy, use the numpy.cbrt() method. The np.cbrt() function returns the cube root of every element of the array. Numpy cbrt() is a mathematical method that is used to find the cube root of every element in a given array.

import numpy as np 

arr1 = [1, 8, 27, 64] 
arr2 = np.cbrt(arr1) 
print(arr2)

Output

[1. 2. 3. 4.]

The np.cbrt() function is the easiest method to calculate a number’s cube root. It does not get in trouble with negative inputs and returns the exact number like 4 for input 64, unlike the above approaches.

That is it for this tutorial.

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Python sqrt

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