Step 1: Convert , which is in radians into degrees. To convert it multiply by
900/12
75
Step 2: 75 degrees isn't on the unit circle but 45 degrees and 30 degrees is. Since 45 + 30 = 75 you can use the cosine of 45 and 30 to find the exact value
cos45 =
cos30 =
Step 3: Add the cos45 and cos30 to get cos5pi/12
Hope this helped!
