Question

What is the first term of the geometric sequence presented in the table below?

n 5 7
an 176 704


Hint: an = a1(r)n − 1, where a1 is the first term and r is the common ratio.

Answer 1

176 = a1 * r^4
704 = a1 * r^6

dividing:-

r^2 = 706/174 = 4 so r = +/- 2

a1 = 176 / 2^4 = 176/16 = 11

So 11 is the first term