SOLUTION: find the exact value of cos 225 degrees

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Question 428088: find the exact value of cos 225 degrees
Answer by lwsshak3(11628) About Me  (Show Source):
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find the exact value of cos 225 degrees
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cos(225)=cos(45+180)
=cos45cos180+sin45sin180
=sqrt(2)/2*(-1)+sqrt(2)*(0)
=-sqrt(2)/2+0
=-sqrt(2)/2