# math!

posted by
**Anonymous** on
.

determine two geometreic sequences whose first terms are 18x-9, 2x+8 and x-1

how would I go about and do this question?

I have no idea! so a little help would be really helpful! thanks!

A geometric sequence looks like

a, ar, ar^{2}, ar^{3}, ..., ar^{n}, ...

where a is usually called the base and r is the common ratio.

If the first three terms are 18x-9, 2x+8 and x-1 then

(2x+8)/(18x-9) = (x-1)/(2x+8)

i.e., the ratio of t_{n}/t_{n-1} is the common ratio.

So solve

(2x+8)*(2x+8)=(18x-9)*(x-1) for x.

Then substitute the values of x into the first 3 terms to determine what they are, then follow the above to determine the common ratio, the base, then the general or n^{th} term.