Step-by-step explanation:
a(n) = a ( n - 1) - 17
a(1) = 20
a(2) = a ( 2 - 1) - 17
= a (1) - 17
= 20 - 17
= 3
Now
a(3) = a ( 3 - 1 ) - 17
= a (2) - 17
= 3 - 17
= - 14
Hope it will help you.
