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Question

Question 21 (ii)
Find the sum:
(41n)+(42n)+(43n)+upto n terms

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Solution

Here, first term, a=41n
Common difference , d=(42n)(41n)=2n+1n=1n
Sum of n terms of an AP, Sn=n2[2a+(n1)d]
Sn=n2[2(41n)+(n1)(1n)]
=n2{82n1+1n}
=n2(71n)=n2×(7n1n)=7n12

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