Proofs
Charles Wheatstone (1854) gives a particularly simple derivation, by expanding each cube in the sum into a set of consecutive odd numbers:
The sum of any set of consecutive odd numbers starting from 1 is a square, and the quantity that is squared is the count of odd numbers in the sum. The latter is easily seen to be a count of the form 1+2+3+4+...+n.
In the more recent mathematical literature, Stein (1971) uses the rectangle-counting interpretation of these numbers to form a geometric proof of the identity (see also Benjamin, Quinn & Wurtz 2006); he observes that it may also be proved easily (but uninformatively) by induction, and states that Toeplitz (1963) provides "an interesting old Arabic proof". Kanim (2004) provides a purely visual proof, Benjamin & Orrison (2002) provide two additional proofs, and Nelsen (1993) gives seven geometric proofs.
Read more about this topic: Squared Triangular Number
Famous quotes containing the word proofs:
“Trifles light as air
Are to the jealous confirmation strong
As proofs of holy writ.”
—William Shakespeare (1564–1616)
“A man’s women folk, whatever their outward show of respect for his merit and authority, always regard him secretly as an ass, and with something akin to pity. His most gaudy sayings and doings seldom deceive them; they see the actual man within, and know him for a shallow and pathetic fellow. In this fact, perhaps, lies one of the best proofs of feminine intelligence, or, as the common phrase makes it, feminine intuition.”
—H.L. (Henry Lewis)
“I do not think that a Physician should be admitted into the College till he could bring proofs of his having cured, in his own person, at least four incurable distempers.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)