Question

12 term of the AS x-2, 4x, 7x+2

Answer 1

Let x-2, 4x, 7x+2 be three first terms of arithmetical sequence. Then
$a_1=x-2, \\ a_2=4x, \\ a_3=7x+2$.
Since $d=a_2-a_1=a_3-a_2$, you receive that $d=4x-(x-2)=7x+2-4x=3x+2$.
The formula for n-th term of arithmetical sequence is: 
$a_n=a_1+(n-1)d$.
Hence $a_{12}=a_1+11d=x-2+11(3x+2)=x-2+33x+22=34x+20$.