Formula for sequence

Question

Find the formula for the sequence -5, -1. 3, 7

Answer 1

a(n)=a+d(n-1) where a=first term and d=common difference

a(n)=-5+4(n-1)

a(n)=-5+4n-4

a(n)=-9+4n for n=1, 2, 3, 4, ...