Question

The third,fourth and fifth terms of GP are t+4 ,t+10 and t+20 respectively. Determine the common ratio,first term and sum of the 12terms

Answer 1

find t using (t+10)^2 = (t+4)(t+20)
having t, r = (t+10)/(t+4)
a = (t+4)/r^2
S12 = a(r^12-1)/(r-1)