CoSinus Matematikk, Forkurs Oppgavesamling by Tore Oldervoll | Goodreads
The history of trigonometric functions - by Tivadar Danka
Pol - Sinus/Cosinus - Amazon.com Music
How to find the measure of an acute, right, or obtuse triangle if only two angles and one side are given - Quora
In simple terms, what do sin, cos and tan mean? How do they relate to a triangle's angles and their respective sides? How are they proportioned to each other? - Quora