SOLUTION: find the exact value of cos 105 degrees WITHOUT USING TABLES OR A CALCULATOR. be sure to show your work.

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Question 41423: find the exact value of cos 105 degrees WITHOUT USING TABLES OR A CALCULATOR. be sure to show your work.
Answer by venugopalramana(3286) About Me  (Show Source):
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find the exact value of cos 105 degrees WITHOUT USING TABLES OR A CALCULATOR. be sure to show your work.
COS(105)=COS(60+45)=COS(60)COS(45)-SIN(60)SIN(45)=(1/2)(1/SQRT2)-(SQRT3/2)(1/SQRT2)
=(1-SQRT(3))/2SQRT(2)=(1-1.732)/(2*1.414)=-0.732/2.828=-0.2588