Question

If the 26th term of an ap is 10.Find the sum of the first 51 terms of the ap

Answer 1

Answer:

Step-by-step explanation:

a26= 10

s51=?

We know that an= a+(n-1)d

So, a26= a+ 25d

=> 10= a+25d

=> a= 10-25d -------1

Now, sn= n/2(2a +(n-1)d)

So s51= 51/2 (2(10-25d) + 50d)

=> s51 = 51/2 (20-50d+50d)

=> s51= 51/2 (20)

s51= 510