3. If cos 2∅= -1/2,find the value of cos∅.
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Answer:
±1/2.
Step-by-step explanation:
cos2∅ = 2(cos ∅)^{2}-1
cos∅ = ±√[(cos2∅+1)/2]
= ±√[(-1/2+1)/2]
= ±√[1/4]
= ±1/2.
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