Constants, Identities, and Variations

(under Construction)

Calculus:

If we have the following conditions:

  1. $f(x)$ is continuous on $[a,b]$,
  2. $f(a)$ and $f(b)$ are of different signs,
Then there exists a point $\xi\in(a,b)$ such that $f(\xi)=0$.

Euler's Formula for Complex Numbers:

$z = cos\ \theta + i\ sin\ \theta = e^{i\theta}$ (standard form)
$z = r (\cos(\theta)+ i \sin(\theta))$ (polar form)
$z = r e^{i\theta}$ (exponential form)
When $\theta = \pi$, Euler's formula evaluates to: $e^{i\pi} + 1 = 0$,

which is known as Euler's Identity

Rational, Irrational, Algebraic, and Transcendental

(as defined in Mathematics - defined elsewhere in other ways)

Rational numbers are expressed as the ratio of two integers or whole numbers: $r=\frac{p}{q}$.

Algebraic numbers are the roots of finite polynomials with integer coefficients: $a_nx^n+\dotsb+a_2x^2+a_1x+a_0=0$.

Every rational number is algebraic when it is a root of the equation $qx-p=0$. There are algebraic numbers which are not rational. The most famous one is $\sqrt2$, which is a root of $x^2-2=0$.

The irrational and transcendental numbers are defined by what they are not: members of $\mathbb R$ in some way:

Every transcendental number is irrational.

That transcendental numbers exist and that not all real numbers are algebraic was first proved by Joseph Liouville  in 1844. The first number to be demonstrably transcendental is now called the Liouville constant:
$\quad\displaystyle\sum_{k=1}^{\infty}10^{-k!}=0.110\,001\,000\,000\,000\,000\,000\,001\,000\dotsc$
The constants $e$ and $\pi$ have been proven to be transcendental, but Transcendental Number Theory has not yet determined whether $e+\pi$ is transcendental.