Answer:
B
Step-by-step explanation:
The double angle formulae for cosine is
cos2x = cos²x - sin²x
[ using sin²x + cos²x = 1 ]
cos2x = cos²x - (1 - cos²x) = cos²x - 1 + cos²x = 2cos²x - 1
Also cos2x = (1 - sin²x) - sin²x = 1 - sin²x - sin²x = 1 - 2sin²x
The double angle formulae are
cos2x = cos²x - sin²x = 2cos² - 1 = 1 - 2sin²x
Hence
cos60° = cos²30° - sin²30°
cos60° = 2cos²30° - 1
cos60° = 1 - 2sin²30°
B is not a representation of cos60°
