14 - 2 = 12 (Difference between 5th term and 1st term)

12 / 4 = 3 (Divide by 4 as there is a difference of 4 terms between the first and fifth)

=> coefficient of n is 3

So far Un = 3n

Using that for the first term gives 3.

2 - 3 = - 1

=> constant is - 1

Therefore:

Un = 3n - 1

(This method only works for linear equations though)