Step-by-step explanation:
T4=a+(4-1)d
a+3d=4.............(1)
T12=a+(12-1)d
a+11d=28..........(2)
using elimination method
3d-11d=4-28
-8d=-24
d=3
substitute d=3 in equation (1)
a+3(3)=4
a=4-9=-5
so the A.P is -5,-2,1,4,7,10,13,16,19,22,25,28...........
