Sum of n terms of an Arithmetic Progression (AP)
An Arithmetic Progression (AP) is a sequence of numbers in which the difference between any two consecutive terms is constant. The sum of the first n terms of an AP can be calculated using the formula:

Sum of n terms of AP = (n/2) * [2a + (n-1)d]
Where:
- a is the first term of the AP
- d is the common difference between the terms
- n is the number of terms to be summed

Given Information
In this case, the 2nd and 8th terms of the AP are equal to a constant value, let's say 'a'. This means that:
- 2nd term = a
- 8th term = a

Finding the common difference
Since the 2nd term is a, and the 8th term is also a, we can find the common difference by subtracting the 2nd term from the 8th term:
a8 = a2 + 6d
a + 6d = a
6d = 0
d = 0

Sum of 1st n terms of the AP
Now that we have found the common difference to be 0, the terms of the AP will all be equal to 'a'. Therefore, the sum of the first n terms of the AP will simply be:
Sum of n terms of AP = n * a
This means that the sum of the first n terms of the given AP is n times the constant value 'a'.