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Question
Using the formula, cos A = `sqrt((1+cos2A)/2) ,`find the value of cos 300, it being given that cos 600 = `1/2`.
Solution
A = 300
⇒ 2A = 2 × 300 = 600
By substituting the value of the given T-ratio, we get:
cos A = `sqrt((1+ cos^2A)/2)`
cos `30^0 = sqrt((1+cos 60^0)/2) = sqrt((1+(1/2)/2)) = sqrt((3/2)/2) =sqrt(3/4) = sqrt(3)/2`
∴ cos A = `sqrt(3)/2`
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