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avatar+1995 
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Dec 13, 2018
 #1
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Dec 13, 2018
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Dec 13, 2018
 #1
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+11

Method of difference

Formula:

nr=1r2=16n(n+1)(2n+1)2nr=1r3=122(2n)2(1+2n)2=n2(1+2n)2

 

nr=1(6r3)2=nr=1(36r236r+9)=36nr=1r236nr=1r+9nr=11=3616n(n+1)(2n+1)36(n+1)2n+9n=6n(n+1)(2n+1)18n(n+1)+9n=6n(n+1)(2n+1)18n218n+9n=6n(n+1)(2n+1)18n29n=3n(2(n+1)(2n+1)6n3)=3n(2(n+1)(2n+1)3(2n+1))=3n(2n+1)(2(n+1)3)=3n(2n+1)(2n1)=3n(4n21)

 

2nr=1r3nr=1(6r3)2=n2(1+2n)23n(4n21)=n2(1+2n)23n(2n1)(2n+1)=n(1+2n)(n(1+2n)3(2n1))=n(1+2n)(n+2n26n+3)=n(1+2n)(2n25n+3)=n(1+2n)(2n3)(n1)

 

laugh

Dec 13, 2018

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