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Question
Find the sum given below:
34 + 32 + 30 + ... + 10
Solution
34 + 32 + 30 + ... + 10
For this A.P.,
a = 34
d = a2 − a1
= 32 − 34
= −2
l = 10
Let 10 be the nth term of this A.P.
l = a + (n − 1) d
10 = 34 + (n − 1) (−2)
−24 = (n − 1) (−2)
12 = n − 1
n = 13
Sn = `n/2(a+1)`
= `13/2(34+10)`
= `(13xx44)/2`
= 13 × 22
= 286
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