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Question
In an A.P., if the first erm is 22, the common difference is -4 and the sum to n terms is -650, find n.
In an A.P., if the first erm is 22, the common difference is -4 and the sum to n terms is -650, find n.
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Solution
Sn=n/2[2a+(n-1)d]
-650=n/2[44+(n-1)(-4)]
-1300=n[44-4n+4]
-1300=48n-4n^2
4n^2-48n-1300=0
n^2-12n+323=0
now solve the equation
Solving for n we get n = -13 and n = 25
as n could never be negative n = 25.
Sn=n/2[2a+(n-1)d]
-650=n/2[44+(n-1)(-4)]
-1300=n[44-4n+4]
-1300=48n-4n^2
4n^2-48n-1300=0
n^2-12n+323=0
now solve the equation
Solving for n we get n = -13 and n = 25
as n could never be negative n = 25.
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