Here's the question you clicked on:
timo86m
I seen many problems like these here http://openstudy.com/study#/updates/5140bf27e4b0f08cbdc91cc0 put what if you where given third term is -96 and 6th term is -6144. its different cuzz you are not giving a as usual. how would you go about solving it? I am just thinking. You'd have to do some kind of system of equations right?
Correct. You would want to find d and a1 by knowing that a3=-96 , and thus n=3, and a6=-6144 and thus n=6.
you would divide n'th term formulas for 3rd and 6th term this will give you common ratio=r then using any of the n'th term formula you can get 'a' also
a3 = a1 r^2 a6 = a1 r^5 if you divide these 2, you get r^3 and hence 'r'
then using a3 = a1 r^2 you can get a1 also
oops, I did t again. I used arithmetic when I should have used geometric. Skip my posts, and go with hartnn's!