Question

The sum of the first 13 terms of an A.P. whose 7th term is 40 is

Answer 1

Answer:

Sum of n terms =n/2(1st term+ nth term).

Let the first term of an A.P. be a and common difference is d.

So the 7th term of the A.P. is 40=> a+6d =40

Sum of first 13 terms = 13/2(a +(a+12d))= 13/2(2a+12d)

=13/2(2)(a+6d) =13(a+6d) =13(40)=520

Step-by-step explanation: