59. For 0° ＜ a° ＜ 90° and 0 ＜ b ＜ 1, when cos a° = b, which of the following expressions is equivalent to cos(2a°) ?
(Note: cos 2θ = (cos θ)2 - (sin θ)2)
Your Answer is
Correct Answer is E
Explanation
cos2a°=(cosa)2-(sina)2=cosa2-[1-(cosa)2 ]=2(cosa)2-1=2b2-1