Please can you prove this?

1+3+3^2+⋯⋯⋯⋯3^(n-1)= (3^n-1)/21+3+32+3n1=3n12

1 Answer
Apr 22, 2018

See explanation

Explanation:

We want to prove

1+3+3^2+...+3^(n-1)=(3^n-1)/2

Let us call

S=1+3+3^2+...+3^(n-1)

Multiply both sides by 3

3S=3+3^2+...+3^(n-1)+3^n

So by the definition of S

3S=(S-1)+3^n

=>2S=3^n-1

=>S=(3^n-1)/2

Or

1+3+3^2+...+3^(n-1)=(3^n-1)/2