If 5+x, 8, and 1+2x are consecutive terms in an arithmetic sequence, find x.

Answer 1

if arithmetic, then

8 - (5+x) = (1+2x) - 8
8 - 5 - x = 1 + 2x - 8
-3x = -10
x = 10/3

check:
terms are 25/3 , 8 , 23/2
or 25/3 , 24/3 , 23/3 which is an AS