Binomial theorem
The binomial theorem has a perfect symmetry, as (a + b)n = (b + a)n.
Explanation
The sum of the binomial theorem is
You can also write this as
That is allowed, because a + b ≡ b + a. This is seen in the binomial coefficients. Written in detail, you get
The series has a perfect symmetry, and you can read it from left to right and from right to left.