# PracticeProve 3^(k + 1) - 1

#### harpazo

##### Pure Mathematics
Banned
Prove that 3^(k+1) − 1 is a multiple of 2.

#### MarkFL

##### La Villa Strangiato
Staff member
Moderator
Math Helper
Assuming $$k\in\mathbb{N}$$ we may write:

$$\displaystyle 3^{k+1}-1=3(2+1)^{k}-1=3\sum_{j=0}^k\left({k \choose j}2^{j}\right)-1=2\left(3\sum_{j=1}^k\left({k \choose j}2^{j-1}\right)+1\right)$$

#### harpazo

##### Pure Mathematics
Banned
Wow! Is there anything in math you don't know?

#### MarkFL

##### La Villa Strangiato
Staff member
Moderator
Math Helper
Wow! Is there anything in math you don't know?
Isaac Newton once said:

"I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

In that analogy, I am far beyond the sand dunes, and if I squint my eyes just right, I can see a boy playing on the shore.

#### harpazo

##### Pure Mathematics
Banned
You certainly fight your way to the right answer. I see this in all your replies.

1. How do you answer math questions when pressured by time (standardized exams)?

2. How fast were you able to complete classroom exams? I do not do well under pressure. The ASVAB, however, was too easy.

3. I can pass the ASVAB today at 53. How about you?

4. Be honest with me. WHY ON EARTH are you not working as a paid math tutor?

Staff member