What is the 9th term of the geometric sequence where a1 = 625 and a3 = 25?

Question

slaaibak · Answer

First get your formula.

ab^n-1

You have the first term, so you can solve a. Then, when you have the a, you can use the third term to solve b.  Then just put 9 into the formula (in n's place)

anonymous · Answer

I am not getting it... so I use a1 as a and a3 as b?

slaaibak · Answer

Nope.  The formula:

$$T _{n}^{}=ab^{n-1}$$


Now, they give you the first term.  

so:

$$T _{1}^{} = ab^{1-1} = 625$$

Now it's possible to get the a value, since b^0 = 1

a = 625.

Now, you need to get b.  

Follow the same steps as I did, but use the third term now. and use the value you just got for a, which is 625