11+9+7+........n terms =-13 then the value of n is
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Answered by
28
Answer:
n = 13
Step-by-step explanation:
11+9+7+........n terms =-13
a = 11
d = -2
Sum of n term = (n/2)(first term + nth term)
(n/2)(a + a +(n-1)d) = -13
n(11 + 11 + (n-1)(-2)) = -26
n(22 -2n +2) = -26
24n - 2n² = -26
12n - n² = -13
n²-12 - 13 = 0
n² -13n + n -13 = 0
n(n-13) +1 (n-13) = 0
(n+1) (n-13) = 0
n = 13 as n can not be negative
Answered by
17
Answer:
Step-by-step explanation:
Simple method
The answer is 13
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