Question

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​

Answer 1

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...........