SEQUENCE AND SERIES A1

The 1st term of a geometric progression is 6 and the 4th term is 48. Find the common ratio.

solution

G₁=6, G₄=48, n=4

G_n = G₁r^n-1;

G₄ = G₁r^4-1;

G₄ = G₁r³;

48 = 6 x r^4-1;

48 = 6 x r³;

48 = 6r³;

 6     6

8 = r³;  Finding the cube root of 8,

r = 2

Hence the common ratio is 2.