Question

The first three term of an A.P are × (3×+1)and(7×-4)

Answer 1

I suppose you want to know what x is, right?

There was no question to your post.

3x+1 - x = 7x-4 - (3x+1) , by definition
2x + 1 = 4x - 5
-2x = -6
x = 3

check:
3, 10, 17 , sure enough! they form an AP