Given is an AP whose first term is - 6 and d is 1/2
To find : the number of terms required to make the sum of a given AP to - 25
We know that the sum of AP is given by the formula :
s = \(\frac{n}{2}\)(2a + (n-1)d)
Substituting the values in the above equation,
- 100 = - 25n + n2
n2 - 25n + 100 = 0
(n - 20) (n - 5) = 0
Solving we get,
n = 20 or n = 5
