How many terms of the A.P. - 6, - , - 5, …, are needed to give the sum - 25?

Question

Philoid · Accepted Answer

given is an AP whose first term is - 6 and d is

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:

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