SOLUTION: Find the exact value of cos(pi) cos(3pi/4) + sin(pi) sin (3pi/4)

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Question 1036513: Find the exact value of cos(pi) cos(3pi/4) + sin(pi) sin (3pi/4)
Found 2 solutions by jim_thompson5910, MathTherapy:
Answer by jim_thompson5910(35256)   (Show Source): You can put this solution on YOUR website!
We'll use the trig identity





use the trig identity (see above)



use the Unit Circle


The final answer is

Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!

Find the exact value of cos(pi) cos(3pi/4) + sin(pi) sin (3pi/4)
This represents the COSINE Difference of 2 angles, as follows: 

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