Question 675196: I need help simplifying the given expression
cos(5)cos(4) + sin(5)sin(4)
Answer by jsmallt9(3758)   (Show Source):
You can put this solution on YOUR website! cos(5)cos(4) + sin(5)sin(4)
cos(A-B) = cos(A)cos(B) + sin(A)sin(B)
Your expression matches the pattern of the right side of cos(A-B), with the "A" being 5 and the "B" being 4. So, according to the formula, your expression must be equal to the left side (with the "A" being 5 and the "B" being 4):
cos(5-4)
which simplifies to:
cos(1)
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