
Actually Welcome to the Concept of the AP.
1.) For the first Sequence, d= 4
so we get as, an = a + (n-1) d
an = 9/2 + (n-1) 4
an = 9/2 +4n -4
=> an = 1/2 + 4n
2.) d = 3
=> an = 10/3 + (n-1) 3
so, => an = 10/3 +3n -3
=> an = 1/3 +3n
3.) d = -0.2
=> an = 1/2 +(n-1) (-0.2)
=> an = 1/2 -0.2n +0.2
=> an= 0.7 -0.2n