All that trigonometry is taught at high school, isn't it? It is but it isn't, my students tell me. Well, the university does not seem the perfect place to teach it but let me take "better here than nowhere" stand.

There are many sites that treat it. Well, one more should do no harm.

If a link does not function, put a blame on my computer. Apparently it did not write the respective part of text. Come back some other day (a week later?) and see where it got any better.

	Relating cos a and sin a to tan(a/2)
	Heron angles