Any geometric sequence can be expressed as:
a(n)=ar^(n-1), a=initial term, r=common ratio, n=term number.
Here we are give the initial term so we have to solve to solve for the common ratio...
a(5)=-1280 and a(1)=-5 so
-1280=-5r^(5-1)
-1280=-5r^4
256=r^4
256^(1/4)=r
4=r, so our sequence is:
a(n)=-5(4^(n-1)), so the 7th term is:
a(7)=-5(4^6)
a(7)= -20480
