hello : the general term is : an = ap×q^(n-p)...... q : common ratio n=5 and p=2 : a5 = a2×q^(5-2) 768 = -12q^3 q^3 = 768/(-12) q^3 = - 64 but : 64 = 4^3 q^3 =(-4)^3.... -4^3 =(- 4)^3 q= - 4 calculate the first term : a1 a2 = a1 q a1 =a2/q a1 = -12/-4 a1 = 3 the sum of the first five terms is : S= a1 × (1- q^n)/(1- q) a1 = 3 q =-4 n =5 S = 3(1-(-4)^5)/(1-(-4)).....calculate
