Just use the formulas you know ...
r^3 = 56/-7 = -8
r = -2
a = -7/r = ____
S5 = a(r^5 - 1)/(r-1)
The 2nd and 5th term of a gp are-7 and 56 respectively. Deduse the common ratio, the first term,the sum of the first five terms?
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