If the sum of first 6 terms of an ap is 36 and that of 11 terms is 121. find the sum of n terms
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Step-by-step explanation:
a = -9 and d = 4
After we have got first term and common difference
Sum of n terms will be =
n/2 [ 2 x -9 + (n - 1) x 4 ]
= n/2 [ -18 + 4n - 4]
= n/2 [ 4n - 22]
After taking 2 common from the bracket
Your final answer is
2n^2 - 11n
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