Question

The third term of a g.p is 12 and the fifth term is 48,find the sum of the first 11 terms

Answer 1

Answer:

G. P

an = a*r^(n-1)

a3 = 12

a*r^(3-1) = 12

a*r^2 = 12 --------(1)

a5 = 48

a*r^(5-1) = 48

ar^4 = 48 --------(2)

(2)/(1);

(ar^4)/(ar^2) = 48/12 = 4

r^2 = 4

r = √4 = 2

substitute r=2 in (1);

a*(2)^2 = 12

4a = 12

a = 12/4 = 3

a = 3

a = 3, r = 2;

r > 1;

so, sn = a(r^n - 1)/(r-1)

s11 = 3((2^11) - 1) /(2-1) = 3((2^11) -1)

s11 = 3((2^11) - 1)

Hope this helps you...