A general geometric sequence has first term a1 and common ratio r. Find
d) an, the general formula for the nth term.
We don't have numbers for a1 and r, but other than that, nothing has changed.
a) a2 = a1r
b) a3 = a2r= a1rr= a1r2
c) a4 = a3r= a1r2r= a1r3
d) Look at the terms we have so far:This means the general formula for the nth term of a geometric sequence isan = a1rn – 1.