Oh shit yes you're right :L I read the question wrong sorry! It's
Which I still have no idea what to do. I think that's a gp though...
How did you get the end numbers again? Carrot tried to explain it on the previous page but i still don't get it :s
So, its best to write our series in expanded form in order to get a good gist of it at first (later on you will become stronger with series and hence be able to spare yourself writing it out expanded form)
So its a Geometric Progression with a common ratio of
(by observation or by dividing any two consecutive terms in the series)
The number of terms is 18
The first term is
Now we are all but ready to plug into our formula, the only thing we have to notice is the difference between
We have to pick which formula to use, now our absolute value of our common ratio is greater than 1 (which is why I specificed that earlier), so we have to use the first formula. Lets plug in our values:
Rationalise our denominator by multiplying both top and bottom by conjugate of denominator