Which of these two form a geometric sequence?
1. 2x, 4x - 2, 6x - 4 .....
2. x + 1, 2x + 2, 5x + 1 .....
check the ratio of successive terms. If it's constant, you have a GP
(4x-2)/2x =?= (6x-4)/(4x-2)
(2x+2)/(x+1) =?= (5x+1)/(2x+2)
Looks like neither to me.