If the 2nd and 5th term of a geometric progression are -6 and 48 respectively. Find the sum of the first four terms.

Answer 1

Use your formulas
ar = -6
ar^4 = 48
divide them:
r^3 = -8
r = -2

now find a, then use the formula for the sum(n) terms
let me know what you get, so I can check it