hello sir, this is soumik... i didnt understand solution to find the double meaning........of the sum from ap (didnt understand the part of double answer from ap) ,i am in 10,the question is as follows....please help me

Consider the A.P. 63, 60, 57, ...

 

Here, a = 63 and d = -3

 

The sum of n terms is given as 693. We need to find 'n'.

 

We know that,

 

The nth term of the series is a + (n - 1)d.

 

Therefore,

 

When n = 22, we have

 

 

Adding 0 to 693 will not change the sum and therefore, the two answers that we are getting are correct.