Find the sum of the series :34 + 32 + 30 +........ + 10 from Ma

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315. Find the sum of the series :
34 + 32 + 30 +........ + 10


Let ‘a’ be the firs term and ‘d’ the common difference, then
a = 34,    d = - 2, a= 10 = l
We know that,  a= a + (n - 1) d
rightwards double arrow   10 = 34 + (n - 1) (- 2)
rightwards double arrow   10 = 34 - 2n + 2
rightwards double arrow   10 = 36 - 2n
rightwards double arrow   - 26 = - 2n
rightwards double arrow      n = 13

And,   S subscript n equals n over 2 left square bracket a space plus space l k right square bracket
S o comma space S subscript 13 equals 13 over 2 left square bracket 34 plus 10 right square bracket equals 13 over 2 cross times 44
equals 13 cross times 22 equals 286
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