Implement 'sin' 'cos' and 'tan' in scheme

[Katie Burke]

Each of these should return the sine, cosine, or tangent of a number.
( http://www.scheme.com/tspl4/objects.html#./objects:s131 )

(sin 0.00)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'sin'

(cos 0.0)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'cos'

(tan 0.0)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'tan'