The 2nd and 5th terms of a GP are -7 and 57 respectively.deduce the common ratio,the first term, the sum of the first five terms

since the two given terms are 3 terms apart,

r^3 = -57/7
so a = -7/∛(57/7) = -7∛(7/57)
S5 = a(r^5-1)/(r-1)