SOLUTION: Find r (common ratio) if a2= 6 and a5= 0.048. I've tried finding r and setting them equal to each other but I have not found a good answer yet.

Algebra ->  Sequences-and-series -> SOLUTION: Find r (common ratio) if a2= 6 and a5= 0.048. I've tried finding r and setting them equal to each other but I have not found a good answer yet.      Log On


   

Question 697719: Find r (common ratio) if a2= 6 and a5= 0.048. I've tried finding r and setting them equal to each other but I have not found a good answer yet.
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
a2= 6 and a5= 0.048
Use the formula:

an = a1r(n-1)

First with n=2

a2 = a1r(2-1)

6 = a1r1

6 = a1r

6%2Fr = a1

And then with n=5

a5 = a1r(5-1)

0.048 = a1r4

0.048%2Fr%5E4 = a1

Equating the expressions for a1

6%2Fr = 0.048%2Fr%5E4

Cross multiplying

6r4 = 0.048r

Divide both side by 6r

r³ = 0.048%2F6

r³ = 0.008

Taking cube roots of both sides

 r = root%283%2C0.008%29

 r = 0.2

Edwin