HELP PLEASE!! really quick!
Find the sum of the first 9 terms of the following sequence: 6, 18, 54.

How do i go about solving this?

Question

HELP PLEASE!! really quick!
Find the sum of the first 9 terms of the following sequence: 6, 18, 54.

How do i go about solving this?

kropot72 · Answer

The formula for the sum of n terms is
$$S _{n}=\frac{a(r ^{n}-1)}{r-1}$$
where a is the first term and r is the common ratio. In this case the common ratio is 3.
Now you just need to plug values into the formula.

anonymous · Answer

Okay, that's what i thought. How do i know what r is? Or rather, how do i figure out r?

kropot72 · Answer

I told you the value of r already. It is found by division of successive terms:
$$r=\frac{18}{6}=?$$

anonymous · Answer

I was just wondering how to figure it out. Is it always the second number divided by the first?

anonymous · Answer

I got 59,046?

kropot72 · Answer

You can find r by dividing any pair of successive terms.
So in the sequence that is given
$$r=\frac{54}{18}$$

anonymous · Answer

Ahhhh, okay. i get it. I got 59,046... Is that right?

kropot72 · Answer

Good work! Your answer is correct.