Why are there two answers for the same problem How is that a

Why are there two answers for the same problem? How is that acheived?

Evaluate each of the following suminations. a) X n +1 1-1 3- 3 Y

Solution

Please note that in the below calculation ( Black ink), you have used the formula of summation of Arithmetic series. The mentioned two series are not Arithmetic. Hence, this formula is not applicable here.

The above calculation (blue ink) is correct.