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Find the sum of series 6^2+7^2+…………………..+15^2.(a) 55(b) 1185(c) 1240(d) 1385I got this question during an online exam.Enquiry is from Sum to n Terms of Special Series topic in division Sequences and Series of Mathematics – Class 11

Answer»

Right CHOICE is (b) 1185

For explanation I WOULD say: 6^2+7^2+………………..…..+15^2

= (1^2+2^2+3^2+……..+15^2) – (1^2+2^2+3^2+4^2+5^2)

= 15*16*31/6 – 5*6*11/6

= 1240-55 = 1185.



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