Geometric series formula when a=1

[tiny-tim]

(just got up :zzz: …)

Bazzinga, you need to learn these two formulas …

for all n:

1 - xⁿ = (1 - x)(1 + x + x² + … + x^n-1)​

for odd n:

1 + xⁿ = (1 + x)(1 - x + x² - … + x^n-1) ​