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# Category Archives: proof

## Ways to prove a bijection

Posted in logic, proof
Tagged bijection, finite, function, injection, invertible, one-to-one, onto, proof, surjection
7 Comments

## A simple proof of the quadratic formula

## A combinatorial proof: PIE a la mode!

Continuing from my last post in this series, we’re trying to show that , where is defined as which is what we get when we start with a sequence of consecutive th powers and repeatedly take successive differences. Recall that … Continue reading

Posted in arithmetic, combinatorics, proof
Tagged consecutive, difference, function, integers, matching, powers

## A combinatorial proof: counting bad functions

In a previous post we derived the following expression: . We are trying to show that , in order to show that starting with a sequence of consecutive th powers and repeatedly taking successive differences will always result in . … Continue reading

Posted in arithmetic, combinatorics, proof
Tagged consecutive, difference, function, integers, matching, powers
1 Comment

## A combinatorial proof: functions and matchings

We’re trying to prove the following equality (see my previous post for a recap of the story so far): In particular we’re trying to show that the two sides of this equation correspond to two different ways to count the … Continue reading

Posted in arithmetic, combinatorics, proof
Tagged consecutive, difference, function, integers, matching, powers
5 Comments

## A combinatorial proof: the story so far

In my last post I reintroduced this seemingly odd phenomenon: Start with consecutive integers and raise them all to the th power. Then repeatedly take pairwise differences (i.e. subtract the first from the second, and the second from the third, … Continue reading

Posted in arithmetic, combinatorics, proof
Tagged consecutive, difference, integers, powers
1 Comment

## A combinatorial proof: reboot!

More than seven years ago I wrote about a curious phenomenon, which I found out about from Patrick Vennebush: if you start with a sequence of consecutive th powers, and repeatedly take pairwise differences, you always end up with , … Continue reading

Posted in arithmetic, combinatorics, proof
Tagged consecutive, difference, integers, powers
11 Comments

## PIE: proof by counting

## PIE: proof by algebra

## Efficiency of repeated squaring: another proof

Posted in computation, proof
Tagged binary, double, efficiency, exponent, increment, proof, repeated, squaring, steps
3 Comments