Over the break post

10.1 formulas for cos(X+B) and sin(X+B)
cos(X+-B)= cosXcosB -+ sinXsinB
sin(X+-B)= sinXcosB+- cosXsinB

Example #1

Find the exact value

Cos75
cos(45+30) X=45 B=30

cos45cos30 - sin45sin30
cos75= the sqaure root of 6 minus the square root of 2 all over 4.

Example #2

Sin15
sin(45-30) X=45 B=30

sin45cos30 - cos45sin30

sin15= the sqaure root of 6 minus the square root of 2 all over 4