arithmetic
posted by Ren on .
How do i find the common ratio, when the 1st, 2nd and 7th terms of a A.P with common difference 2 are the first three terms of a G.P .

The first, second, and seventh terms of your AP would be
a, a+2, and a+12
but these are supposed to be the first 3 terms of a GP, so
(x+2)/a = (a+12)/(a+2)
crossmultiply, the a^2 drops out and you get
a = 1/2
now you know your first 3 terms of the GP to be
1/2, 5/2, and 25/2
check for common ratio:
(5/2) ÷ (1/2) = 5
(25/2) ÷ (5/2) = 5 
(x+2)/a = (a+12)/(a+2)
obviously should have been
(a+2)/a = (a+12)/(a+2) 
Hey thanks a lot Reiny. I got it..