9514 1404 393
Answer:
22. E
23. C
Explanation:
These questions are asking you to make use of a couple of trig identities for converting products to sums.
sin(x)cos(y) = 1/2(sin(x+y) +sin(x -y))
cos(x)cos(y) = 1/2(cos(x+y) +cos(x -y))
sin(-x) = -sin(x)
cos(-x) = cos(x)
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22. sin(2β/3)cos(4β/3) = (1/2)(sin((2+4)β/3) +sin((2-4)β/3))
= 1/2sin(2β) +1/2sin(-2β/3) = 1/2sin(2β) -1/2sin(2β/3)
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23. cos(3θ)cos(5θ) = (1/2)(cos(3θ+5θ) +cos(3θ -5θ)) = 1/2cos(8θ)+1/2cos(2θ)