Sum of the series n∑r=11(ar+b)(ar+a+b), (where a≠0) is
A
n(a+b)[a(n+1)+b]
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B
n(a+b)[an+b]
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C
n(a+b)[a(n−1)+b]
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D
n(a+b)[a(n+2)+b]
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Solution
The correct option is An(a+b)[a(n+1)+b] 1(ar+b)(ar+a+b)=1a[1ar+b−1ar+a+b] n∑r=11(ar+b)(ar+a+b)=n∑r=11a[1ar+b−1ar+a+b]=1a[1a+b−1a+a+b]+1a[12a+b−12a+a+b]+1a[13a+b−13a+a+b]+⋮⋮+1a[1an+b−1an+a+b]Sn=1a[1a+b−1a(n+1)+b]=n(a+b)[a(n+1)+b]