# Mathematics

This is such an undescriptive title because there is so much covered under this branch

Mathematics is such a broad term for what I want to cover. There are many that are broken out that should be covered under this but I digress. These are concepts based in mathematics which may or may not have practical applications in the real world. But in any case, I think that my favorite is stuff that everyone can at least be somewhat familiar with.

## Screwing Around

A fun example is that two concepts that are taught in high school are intimately related to each other: the quadratic formula can be derived by completing the square of a generic quadratic equation.

Even though these symbols are interchangeable, by manipulating them in the same context, the

### Alternating Summation of Ones

Here is a pretty common high school problem that shows the weirdness that happen with infinite series.

We want to know what the value is so set equal to some unknown, like $\text{X}$ and notice that it contains itself.

### Divisibility Tricks

Ran into a situation where you needed to know if a number had a specfic factor? Here are some fast ways check the divisibility of large numbers, courtesy of reddit user u/BlueEmu. Remember that you can also check divisibility by larger numbers using factors. A number divisible by 15 would be divisible by both 3 and 5.

Divisor | Rule |
---|---|

1 | ...all numbers are divisible by 1 |

2 | Last digit is even |

3 | Sum of the digits is divisible by 3 |

4 | Last two digits are divisible by 4 |

5 | Last digit ends in 0 or 5 |

6 | Satisfies both 2 and 3 |

8 | Last three digits divisible by 8 |

9 | Sum of the digits are divisible by 9 |

## Links

Last updated