Find the recursive formula ... 3, - 7, - 17, - 27, ...

The negative sign isnt changing back and forth, so its not a geometric sequence

the difference between each term looks to be constant at 10

a1 = 3

a2=-7 = a1-10

a3 = - 17 = a2-10

oh look a pattern

an = a (n-1) - 10