[[$ a^2 + b^2 = c^2 $]] (Pythagorean theorem)

[[$ A = \dfrac{1}{2}ab $]]

Trigonometric functions

[[$ \text{sin} \space \alpha = \dfrac{a}{c}, \text{cos}\space\alpha = \dfrac{b}{c}, \text{tan} \space \alpha = \dfrac{a}{b} $]]​