The second term of a gp is , while the fourth term is 81.find:
1.the common ratio of the first term
2.the first five terms of the sequence
bogus subject
incomplete question.
garbled question: "common ratio of the first term" makes no sense.
But, r^2 = a4/a2
since 81 = 9^2, I'm guessing a2 = 9, r=±3
now work out the rest, using the GP formulas you have.