cos 40 + cos 80 + cos + 180
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Answer:
cos 40 + cos 80 + cos 160 + cos 240
=2cos(
2
40+80
)cos(
2
40−80
)+cos(180−20)+cos(180+60)
=2cos60.cos(−20)+(−cos20)+(−cos60)
∵cosC+cosD=2cos(
2
C+D
).cos(
2
C−D
)
cos(180+θ)=−cosθ
cos(180−θ)=−cosθ
=2×
2
1
cos(20)−cos(20)−
2
1
(cos(−θ)=cosθ)
=cos20−cos20−
2
1
=−
2
1
Step-by-step explanation:
please make me brainlist please thanks