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  • Let Sn denote the sum of the first n terms of an A.P, a1, a2, a3,......an. If a5 + a9 = 1 and S9 = 6, then which of the

Let Sn denote the sum of the first n terms of an A.P, a1, a2, a3,......an. If a5 + a9 = 1 and S9 = 6, then which of the following is not true?

Option: 1

a13 = 0


Option: 2

S13 = 13/2


Option: 3

s6 = - 19/4


Option: 4

a6 + a8 = 1


Answers (1)

best_answer

Sum of n terms of an AP -

\begin{array}{l}{S_{n}=\frac{n}{2}[2 a+(n-1) d]} \\ {\text { OR }} \\ {S_{n}=\frac{n}{2}[a+l]} \\ {a \rightarrow \text { first term }} \\ {d \rightarrow \text { common difference }} \\ {n \rightarrow \text { number of terms }}\end{array}

 

Given,

S6 = 3 ( 2 + 5(-1/12)) = -19/4

Posted by

vinayak

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