SOLUTION: what is the value of the following function? cos(130°)cos(10°) + sin(10°) sin(130°).

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Question 449095:
what is the value of the following function? cos(130°)cos(10°) + sin(10°) sin(130°).
Answer by lwsshak3(11628) About Me  (Show Source):
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what is the value of the following function? cos(130°)cos(10°) + sin(10°) sin(130°).
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Addition formula for cosine:
cos(s-t)=cos s cos t+sin s sin t
For given equation:
cos(130°)cos(10°) + sin(130°) sin(10°)=cos(130º-10º)=cos 120º
In standard position 120º terminates in quadrant II where cos is negative.
reference angle=180-120 =60º
cos 60º=-1/2