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 Let a1,a2an be the terms of an A.P. a1+a2+apa1+a2++a1=p2q2,pq.  Then a6a21=

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a
1141
b
1127
c
1259
d
1631

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detailed solution

Correct option is A

p22a1+(p−1)dq22a1+(q−1)d=p2q2⇒2a1+(p−1)d2a1+(q−1)d=pq⇒a1+p−12da1+q−12d=pq For a6a21,p=11,q=41⇒a6a21=1141 where p−12=5 p=11q−12=20 q=41


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If the sum of first n terms of an AP is cn2, then the sum of squares of these  n terms is 


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