SOLUTION: Using one of the sum and difference identities, find the exact value of: cos(30{{{degrees}}}+45{{{degrees}}})

Algebra ->  Trigonometry-basics -> SOLUTION: Using one of the sum and difference identities, find the exact value of: cos(30{{{degrees}}}+45{{{degrees}}})      Log On


   

Question 682759: Using one of the sum and difference identities, find the exact value of:
cos(30degrees+45degrees)
Answer by funmath(2933) About Me  (Show Source):
You can put this solution on YOUR website!
highlight%28cos%28a%2Bb%29=cos%28a%29cos%28b%29-sin%28a%29sin%28b%29%29
cos%2830%2B45%29=cos%2830%29cos%2845%29-sin%2830%29sin%2845%29
Use your unit circle or 45,45,90 and 30,60,90 triangles to evaluate:
cos%2830%2B45%29=%28sqrt%283%29%2F2%29%28sqrt%282%29%2F2%29-%281%2F2%29%28sqrt%282%29%2F2%29
Simplify:
highlight%28cos%2830%2B45%29=%28sqrt%286%29-sqrt%282%29%29%2F4%29