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Question
Find the value of x , if `cosx = cos60^circ cos30^circ - sin60^circ sin30^circ`
Solution
`cos(2x - 6)= cos^2 30^circ - cos^2 60^circ`
⇒ `cos(2x - 6) = cos^2(90^circ - 60^circ) - cos^2 60^circ`
⇒ `cos(2x - 6) = sin^2 60^circ - cos^2 60^circ`
⇒ `cos(2x - 6) = 1 - 2cos^2 60^circ = 1 - 2(1/2)^2 = 1 - 1/2 = 1/2`
⇒ `cos(2x - 6) = 1/2`
⇒ `cos(2x - 6) = cos60^circ`
⇒ `(2x - 6) = 60^circ`
⇒ `2x = 66^circ`
⇒ `x = 33^circ`
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