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If Sn=r=1ntr=16n2n2+9n+13, then r=1ntrequals

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a
12n(n+1)
b
12n(n+2)
c
12n(n+3)
d
12n(n+5)

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detailed solution

Correct option is C

We have tn=Sn−Sn−1∀n≥2∴ tn=16n2n2+9n+13−16(n−1)2(n−1)2            =162n3−(n−1)3+9n2−(n−1)2           =166n2−6n+2+9(2n−1)+13           =166n2+12n+6            =(n+1)2Also,  t1=S1=4=(1+1)2∴   ∑r=1n tr=∑r=1n (r+1)=12(n+1)(n+2)−1=12n(n+3)


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