show that cos (-330)cos 420=√3/4
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Answer:
Step-by-step explanation:
Cos(-330)Cos420
//Cos(-θ) = Cosθ
Cos(-330) = Cos330 = Cos(360 - 30) = Cos30 = √3/2 (Cosine in 4th quadrant, Cos is positive here)
Cos420 = Cos(360 + 60) = Cos60 = 1/2 ( Cosine is in first quadrant, so all positive)
=> √3/2 * 1/2
=> √3/4.
=> R.H.S
Hence proved.
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