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1^3 + 2^3 + 3^3 + 4^3 + 5^3 +.... 2014^3

 Aug 10, 2014

Best Answer 

 #4
avatar+33654 
+8

It's not at all obvious!  But have a look at https://proofwiki.org/wiki/Sum_of_Sequence_of_Cubes for a proof. 

 Aug 10, 2014
 #1
avatar+118703 
+8

You can probably do this on the web2 calc as well but i don't know how.

anyway, I got you the answer. 

 

 Aug 10, 2014
 #2
avatar+33654 
+8

Can find this from:

nk=1k3=n2(n+1)24

(2014×2015)24=4117267101025

 Aug 10, 2014
 #3
avatar+118703 
+3

Why is that true Alan?

Is there something obvious that I am missing?

 Aug 10, 2014
 #4
avatar+33654 
+8
Best Answer

It's not at all obvious!  But have a look at https://proofwiki.org/wiki/Sum_of_Sequence_of_Cubes for a proof. 

Alan Aug 10, 2014
 #5
avatar+118703 
+3

Thanks Alan,

I'll spend more time in it. 

 Aug 10, 2014
 #6
avatar+26396 
0

1^3 + 2^3 + 3^3 + 4^3 + 5^3 +.... 2014^3  

 

s1=1+2+3+...+n

\begin{array}{llcl}  & (1+i)^2 &=& i^2+2i+1 \\  & (1+i)^2 - 1 &=& 1+2i \\  \hline  i=1 & \not{2^2}-1^2 &=& 1+ 2*1\\  i=2 & \not{3^2}-\not{2^2} &=& 1+ 2*2 \\  i=3 & \not{4^2}-\not{3^2} &=& 1+ 2*3 \\  ... &... &...& ... \\  i=n & (1+n)^2-\not{n^2} &=& 1+2n\\  \hline  \Sigma & (1+n)^2-1&=&n+2*(\underbrace{1+2+3+...+n}_{s_1})  \end{array}\\  (1+n)^2-1&=&n+2s_1\\  n+n^2=2s_1\\  \boxed{s_1=\dfrac{n(n+1)}{2}}

 

s2=12+22+32+...+n2

(1+i)3=i3+3i2+3i+1(1+i)3i3=1+3i2+3ii=12313=1+312+31i=23323=1+322+32i=34333=1+332+33............i=n(1+n)3n3=1+3n2+3nΣ(1+n)31=n+3(12+22+32+...+n2s2)+3(1+2+3+...+ns1)(1+n)31=n+3s2+3s1(1+n)31=n+3s2+3n(n+1)2s2=n(16+n2+n23)s2=n6(1+3n+2n2)s2=n6(n+1)(2n+1)

 

s3=13+23+33+...+n3

(1+i)4=i4+4i3+6i2+4i+1(1+i)4i4=1+4i3+6i2+4ii=12414=1+413+612+41i=23424=1+423+622+42i=34434=1+433+632+43............i=n(1+n)4n4=1+4n3+6n2+4nΣ(1+n)41=n+4(13+23+33+...+n3s3)+6(12+22+32+...+n2s2)+4(1+2+3+...+ns1)(1+n)41=n+4s3+6s2+4s1(1+n)41=n+4s3+6n6(n+1)(2n+1)+4n(n+1)24s3=n4+4n3+6n2+4nn2n33n2n2n22n4s3=n4+2n3+n2s3=n2(n+1)24

13+23+33+43+53+....20143=(201420152)2=20291052=4117267101025

 Aug 21, 2014

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