Interesting Maths
$$ f(a)=\frac{1}{2\pi i} \oint_\Gamma \frac{f(z)}{z-a}dz $$
Group Theory: the study of groups,
a complex mathematical structure that applies to many different fields.
Examples include Rubik's Cube, Symmetries of a Triangle, Real Numbers, Complex Numbers, Matrices, and more.
$$
\def\diagUpArrow#1{\smash{
\raise.6em\rlap{\scriptstyle #1}
\lower.3em{\mathord{\diagup}}
\raise.52em{\!\mathord{\nearrow}}
}}
\def\diagDownArrow#1{\smash{
\raise.5em\rlap{\ \ \ \scriptstyle #1}
\raise.3em{\mathord{\diagdown}}
\lower.52em{\!\mathord{\searrow}}
}}
\begin{CD}
{R} @> {f} >> {G_1} \\
@V{g}VV @AA{\zeta}A \\
{G_2} @>>{\tau}> {D_n} \\
&&& \diagDownArrow{\gamma} \\
&&&& {M}
\end{CD}
$$
Surface Integrals: a complex topic from calculus that brings together everything else. It finds surface area. It relates to fluids, vectors, electricity and magnetism, and more. It also has a fun name, flux.