Question

find the sum of n terms of the AP a,A + D,a + 2D...a+​

Answer 1

Solution :

The AP is given by

a, a + d, a + 2d, a + 3d, ...

whose first term is a and the common difference is d

Then, the nth term

= a + (n - 1)d

Now, sum of n terms

= n/2 [ first term + nth term ]

= n/2 [ a + a + (n - 1)d ]

= n/2 [ 2a + (n - 1)d ] (Ans.)