Question

the sum of three numbers in g.p is 21 and sum of their squares is 189 find the sum of its first n terms is

Answer 1

let the first number X .Then second number is equal to [X+1] third number is equal to (X + 2)

so, X + X + 1 + X + 2 equal to 21
x=6
show the first and third is 6