Question

if x-1,x+3,3x-1 are in A. p then x=?

Answer 1

they are in ap so their common difference will be equal
x+3-(x-1)=3x-1-(x+3)
x+3-x+1=3x-1-x-3
4=2x-4
2x=8
x=4

Answer 2

We know that an AP have common difference between adjacent terms

a2-a1=a3-a2

(x+3)-(x-1)=(3x-1)-(x+3)
x+3-x+1=3x-1-x-3
4=2x-4
2x=8
x=8/2=4

Hope that this helps you (^_^)b