Wednesday, January 12, 2022

 

Fun with numbers - All about cubes 

The cubes have some amazing numerical characteristics. 

13 = 1 (one odd )

23 = 3 + 5 = 8 (two successive odds)

   = 1x2 + 1 + 2x3 -1

   = (22 -1)  + (22 = 1)

33 = 7 + 9 + 11 = 27 (three successive odds)

   =( 2x3 + 1)  + ……+(3 x4 -1)

   = (32 – 2) + 32 + (32 +2)

43 = 13+15+17+19  = 64 (Four succesivve odds)

   = (3x4+1) +……… +(4x5 -21)

  = (42 -3) +(42 – 1) +(42+ 1) + (42 + 3) 

53 = 21 + 23 + 25+ 27 + 29 = 125 (Five successiver odds)

   = (4x5 +1) +………….+ )5x6 – 1)

   = (52 -4) + (52 – 2) + 52 + (52+ 2) + (52 + 4)

In general  

,n3 = ((n-1)n +1]+ ----------- + [n(n+1) -1]

     =(n2 – n + 1)+ …………..+ (n2 + n -1) 

Another property of cubes 

13  = 6(0) + 1

23 = 13 + 6(1) + 1  = 6(1) + 2

32 = 23 + 6(3) + 1 =  6(4) + 3

43 = 33  + 6(6) + 1 = 6(10) + 4

53 = 43  + 6(10)+ 1 = 6(20) + 5

63 = 53 + 6(15) + 1 = 6(35) + 6 = 6(36)+ 0 

In general 

,n3 = (n-1)3 +6 [n(n-1)/2} + 1 = 6 [ 1n Σ n(n-1)/2] + n

 

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