Python/maths/sum_of_geometric_progression.py

def sum_of_geometric_progression(
    first_term: int, common_ratio: int, num_of_terms: int
) -> float:
    """ "
    Return the sum of n terms in a geometric progression.
    >>> sum_of_geometric_progression(1, 2, 10)
    1023.0
    >>> sum_of_geometric_progression(1, 10, 5)
    11111.0
    >>> sum_of_geometric_progression(0, 2, 10)
    0.0
    >>> sum_of_geometric_progression(1, 0, 10)
    1.0
    >>> sum_of_geometric_progression(1, 2, 0)
    -0.0
    >>> sum_of_geometric_progression(-1, 2, 10)
    -1023.0
    >>> sum_of_geometric_progression(1, -2, 10)
    -341.0
    >>> sum_of_geometric_progression(1, 2, -10)
    -0.9990234375
    """
    if common_ratio == 1:
        # Formula for sum if common ratio is 1
        return num_of_terms * first_term

    # Formula for finding sum of n terms of a GeometricProgression
    return (first_term / (1 - common_ratio)) * (1 - common_ratio**num_of_terms)