Re: [math-fun] Proofs without words

See Conway & Guy, The Book of Numbers. On Mon, 31 Dec 2007, Dan Asimov wrote:

Can someone please point me to proofs without words for

a) nth tetrahedral number = n(n+1)(n+2)/6

b) sum of the first n squares = n(n+1)(2n+1)/6

c) sum of the first n cubes = (sum of first n numbers)^2 = (T_n)^2 (T_n = nth triangular #) ?

Thanks,

Dan

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