Teaching Kids Programming – Sum of Geometric Progression (Math Proof and Python Function)

ACMer

4 years ago

Teaching Kids Programming: Videos on Data Structures and Algorithms

Geometric Progression of numbers are:

where q is neither 1 or 0. We want to compute the sum, aka

Let where , and
Multiple both sides with q (since q can’t be zero)

which is
We can subtract both side from aka

Therefore

Here is the simple python function to compute the sum of a geometric progression.

def sum(a, q, n):
    s = 0
    for i in range(n):
        s += a * (q ** i)
    return s

We can also use math.pow(q, i) to compute the value of q to the power of i.