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Sagot :
Answer:
b
Step-by-step explanation:
use cos(r + s ) = cosrcoss - sinrsins to expand.
cos pi/3 cosx - sin pi/3 sinx + cos pi/3 cosx + sin pi/3 sinx
the two in bold cancel out.
cospi/3 cosx + cospi/3 cosx
pi = 180° in trigonometry.
cos 180/3 cosx + cos 180/3 cosx
1/2 cosx + 1/2 cosx
= cos x
- cos(A+B)+cos(A-B)=2cosAcosB
Hence
- cos(π/3+x)+cos(π/3-x)
- 2cosπ/3(cosx)
- 2(1/2)(cosx)
- cosx
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