# Homework Help: Geometric progression

1. Aug 11, 2011

### nae99

1. The problem statement, all variables and given/known data

3,6,12........1536
determine the number of terms in the progression

2. Relevant equations

3. The attempt at a solution
a=3 r=2

n= ar^n-1

1536= (3) (2)^n-1

2. Aug 11, 2011

### HallsofIvy

Okay, so solve it! First, divide both sides by 3. If that sequence is actually geometric, you should be able to identify 1536/3 as a power of 2. I suggest you just calculate powers of 2: 1, 2, 4, 8, 16, ... until you get to that number.

3. Aug 11, 2011

### nae99

1536= (3) (2)^n-1

1536/3 = 6^n-1$/$3

512 = 2^n-1

512 = 2^10-1

512 = 2^9

n = 10

4. Aug 11, 2011

### Staff: Mentor

There are errors in your work. Also, you need parentheses around your exponent expressions.
The above is incorrect. 3*2^(n - 1) $\neq$ 6^(n - 1)
The above is also incorrect. [6^(n - 1)]/3 $\neq$ 2^(n - 1)