These are values that you should know by heart. For other angles, you should be able to find the sine and cosine values using a calculator or a table.
1
sin 45 deg = opp / hyp = -----------
sqrt(2)
cos 45 deg = adj / hyp = (same as above)
sqrt(3)
Note that sin 30 deg = 1/2, and that cos 30 deg = ------------
2