Right Triangle

Once upon a time there was little Hypotenuse. He had two cousins: the Opposite and his sister the Adjacent. Both were usually just known by their nick names 'Sine'^[2] and 'Cosine'^[3]. They lived together in a right triangle close to the woods. They were related through his mother's sister, aunty Alpha. His father, who was a mathematician, used to say that:

${\displaystyle \sin \alpha ={\frac {\textrm {opposite}}{\textrm {hypotenuse}}}={\frac {a}{h}}}$

${\displaystyle \cos \alpha ={\frac {\textrm {adjacent}}{\textrm {hypotenuse}}}={\frac {b}{h}}.}$

Sometimes he also referred to uncle Tangent (who was married to aunty Alpha) and said that

${\displaystyle \tan \alpha ={\frac {\textrm {opposite}}{\textrm {adjacent}}}={\frac {a}{b}},}$

so in a sense uncle Tangent of aunty Alpha was Sine divided by Cosine. To us that didn't make any sense, but Hypotenuse's father said that was how it always was.

Vectors

Matrices

References