The formula for any geometric sequence is an = a1 · rn - 1, where a n represents the value of the n th term, a1 represents the value of the first term, r represents the common ratio, and n represents the term number. What is the formula for the sequence - 3, - 6, - 12, - 24, ... ?

You'd be better off if you'd invest a bit more time into presenting that formula for a geometric sequence. rn-1 is 'way off base.

Instead, try making the subscripts and superscripts stand out:

n-1

a = a * r

n n-1

Believe me, it's worth the extra work to do this!

Given the sequence - 3, - 6, - 12, - 24, you can easily see that the first term,

a is - 3. The common factor is 2. Note how (-3) * 2=-6, and so on.

1

So, a = - 3 and r=2.

1

So the formula for this geometric sequence is

n-1

a = - 3*2

n