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360 degrees = 2p radians
so, 180 degrees = p radians

The original angle can be found by using the inverse trig function. For example:

Sometimes in the literature, arcsin is written as sin^-1 and so on to indicate that it is an inverse function.

In the following examples, the side lengths are found using the Pythagorean theorem.

sin 45^o = cos 45^o = 1/1.4142 = 0.7071
tan 45^o = cot 45^o = 1/1 = 1

sin 30^o = cos 60^o = 1/2 = 0.5
cos 30^o = sin 60^o = 1.7321/2 = 0.8661
tan 30^o = cot 60^o = 1/1.7321 = 0.5774
cot 30^o = tan 60^o = 1.7321/1 = 1.7321

Then, there are the special cases of 0 and 90^o.

The sin and cos for the full circle (0 to 360^o) are spelled out in the quadrant trigonometry facts help page.