Triangle Breakdown

A fundamental realization. Not all 3 lines of a triangle are equal. It's really a relationshop of 2 and 1.

By definition, a hypotenuse line is nothing more than a composite vector (or a 'child' you could say) of one x-axis vector and one y-axis vector.

In other words, all hypotenuses are made up of adjacents and opposites but adjacents and opposites (running parallel to the axis') are not made up of hypotenuse lines.

Note then that sine and cosine are essentially אבות of the tangent. Note also the often interchanging/interweaving (התכללות) of sine and cosine together in various areas (their derivatives for example), moreso than with tangent.