Question

15. What is the common difference of an AP in which a21-a7=28​

Answer 1

Given :

In A.P a relation , $A_{21}-A_7=28$   ......1 )

To Find :

Common difference of A.P .

Solution :

We know , n th term in A.P is given by :

$a_n=a_1+(n-1)d$

Now , putting value of $A_{21}$ and $A_7$ in equation 1 , we get :

$[a_1+(21-1)d]-[a_1+(7-1)d]=28\\\\20d-6d=28\\\\14d=28\\\\d=2$

Therefore , common difference is 2 .

Hence , this is the required solution .