I tell my students that they should know them almost

When teaching the unit circle I always begin with special right triangles, but once that foundation is laid, I use this left hand trick. You can find the notes here.

*as**fast as their multiplication facts*. The ones who succeed always do well with the remainder of trigonometry.
This is SO much quicker than drawing tiny special right triangles for every problem.

Quick tip:

**I also emphasis that tangent (opposite/adjacent) is really just slope**. Every student should know the slope of a vertical, horizontal and 45 degree lines, so they really know tangent of the quadrantal angles and all of the angles with a reference angle measurement of 45 degrees.