How many terms of the AP -6,-11/2,-5...are needed to give the sum -25 ??
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Step-by-step explanation:
a = -6, d = 1/2, sum = -25 Sn = n/2 * (2a + (n-1)*d) ....
-25 = n/2 * (-12 + (n-1)*1/2) ...
-50 = n*( -24 + n -1 )/2
-100 = n* (n-25)
-100 = n^2 - 25n
n^2 - 25n + 100 = 0
sum = -25
Product = 100
The numbers are -20, -5
n^2 -20n -5n +100 = 0
n(n-20) -5(n-20) = 0
(n-5)*(n-20) = 0
n = 5 or n=20
For the first time the sum to be -25, we need to take only 5 terms
Anonymous:
Even if we take 20 terms we will get the sum to be -25 since it is an increasing A.P from negative to positive
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