Question

Question 11 :
(a) The sum of 3rd and 11th terms of an A.P. is 34. Find the sum of its 13 term .​

Answer 1

Step-by-step explanation:

We know that

third term = a+2d----------a

and

11th term = a+10d---------b

now

a+b = 2a+12d = 34--------(given)

now sum of 13 terms is

Sn = S13 = 13/2×[2a+12d]

S13 = 13/2×34---------[2a+12d = 34]

therefore S13 = 13×17=221 Answer