# How to subtract one polynomial to another using NumPy in Python?

• Last Updated : 29 Aug, 2020

In this article, let’s discuss how to subtract one polynomial to another. Two polynomials are given as input and the result is the subtraction of two polynomials.

• The polynomial p(x) = C3 x2 + C2 x + C1  is represented in NumPy as : ( C1, C2, C3 ) { the coefficients (constants)}.
• Let take two polynomials p(x) and q(x) then subtract these to get r(x) = p(x) – q(x) as a result of subtraction of two input polynomials.
```If p(x) = A3 x2 + A2 x + A1
and
q(x) = B3 x2 + B2 x + B1

then result is
r(x) = p(x) - q(x) i.e;
r(x) = (A3 - B3) x2 + (A2 - B2) x + (A1 - B1)

and output is
( (A1 - B1), (A2 - B2), (A3 - B3) ).
```

In NumPy, it can be solved using the polysub() method. This function helps to find the difference of two polynomials and then returning the result as a polynomial

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Below is the implementation with some examples :

Example 1:  Using  polysub()

## Python3

 `# importing package``import` `numpy`` ` `# define the polynomials``# p(x) = 5(x**2) + (-2)x +5``px ``=` `(``5``,``-``2``,``5``)`` ` `# q(x) = 2(x**2) + (-5)x +2``qx ``=` `(``2``,``-``5``,``2``)`` ` `# subtract the polynomials``rx ``=` `numpy.polynomial.polynomial.polysub(px,qx)`` ` `# print the resultant polynomial``print``(rx)`

Output :

`[ 3.  3.  3.]`

Example 2: sub_with_decimals

## Python3

 `# importing package``import` `numpy`` ` `# define the polynomials``# p(x) = 2.2``px ``=` `(``0``,``0``,``2.2``)`` ` `# q(x) = 9.8(x**2) + 4``qx ``=` `(``9.8``,``0``,``4``)`` ` `# subtract the polynomials``rx ``=` `numpy.polynomial.polynomial.polysub(px,qx)`` ` `# print the resultant polynomial``print``(rx)`

Output :

```[-9.8  0.  -1.8]
```

Example 3:  #eval_then_sub

## Python3

 `# importing package``import` `numpy`` ` `# define the polynomials``# p(x) = (5/3)x``px ``=` `(``0``,``5``/``3``,``0``)`` ` `# q(x) = (-7/4)(x**2) + (9/5)``qx ``=` `(``-``7``/``4``,``0``,``9``/``5``)`` ` `# subtract the polynomials``rx ``=` `numpy.polynomial.polynomial.polysub(px,qx)`` ` `# print the resultant polynomial``print``(rx)`

Output :

```[ 1.75        1.66666667 -1.8       ]
```

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