Question

How many terms of AP -6,-11/2,-5...are needed to give the sum of -25?
Explain the double answer.

Answer 1

Answer

Step-by-step explanation:

Answer 2

Answer:

Step-by-step explanation:

Solution :-

A.P. is - 6, - 11/2, - 5, ....

Then, a = - 6

d = - 11/2 + 6/2 = 1/2

and S (n) = - 25

or, S(n) = n/2[2a + (n - 1)d]

Hence, - 25 = n/2[- 12 + (n - 1) × 1/2]

or, - 50 = n[- 24 + (n - 1)/2]

or, - 100 = n[n - 25]

or, n² - 25n + 100 = 0

or, (n - 20) (n - 5) = 0

or, n = 20, 5

or, S(20) = S(5)

Two Answer,

a is negative and d is positive and the sum of the terms from 5th to 20th is zero.