sin 2A
A
(i)
(1-сos A)
cos A
= tan
2
(1-cos2A)
2
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Step-by-step explanation:
How to proof the formula of cos 2A is equals 2 cos22 A - 1? (ii) In the above formula we should note that the angle on the R.H.S. is half of the angle on L.H.S. Therefore, cos 120° = cos22 60° - sin22 60°. (iii) The above formulae is also known as double angle formulae for cos 2A.
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