Prove that cos (60°_30°)=cos 60°cos 30°+sin 60° sin 30°•
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1
Answer:
it is the double angle formula
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0
i think all the sign should be positive
Step-by-step explanation:
cos(60+30)=cos60cos30-sin60sin30
cos(90)=cos60cos(90-60)-sin60sin(90-60)
cos90=cos60.sin60-sin60.cos60
cos90=0
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