The sum of the first 4 terms of an A. P is 4, the sum of the first 12 terms is 28. Find the A. P

Step-by-step explanation:

let the A.P. be a,a+d,a+2d,a+3d,a+4d,...

multiply (1) by 3

6a+9d=12   ...(3)

(2)-(3)  gives

24d=2

d=2/24=1/12

from (1)

2a+3(1/12)=4

2a=4-1/4=15/4

a=15/8

a+d=15/8+1/12=(45+2)/24=47/24

a+2d=15/8+2(1/12)=15/8+1/6=(45+4)/24=49/24

so A.P. is 15/8,47/24,49/24,....