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Question

Question 2 (i)
Find the sums given below
(i) 7+1012+14++84

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Solution

(i)
For this A.P.,
a = 7
an=84
d=a2a1=10127=2127=72
Let 84 be the nth term of this A.P.
an=a+(n1)d84=7+(n1)×7277=(n1)×7222=n1n=23We know that,Sn=n2(a+an)S23=232(7+84)=(23×912)=20932=104612

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