精品文档 正弦二倍角公式: sin2α = 2cosαsinα 推导: sin2α = sin(α+α) = sinαcosα + cosαsinα= 2sinαcosα 余弦二倍角公式: 余弦二倍角公式有三组表示形式,三组形式等价: 1.cos2α = 2cos^2 α- 1 2.cos2α = 1 − 2sin^2 α 3.cos2α = cos^2 α − sin^2 α 推导: cos2A = cos(A+A) = cosAcosA - sinAsinA = cos^2 A- sin^2 A = 2cos^2 A - 1=1 - 2sin^2 A 正切二倍角公式: tan2α = 2tanα/[1 - (tanα)^2] tan(1/2*α)=(sin α)/(1+cos α)=(1-cos α)/sin α 推导: tan(2a) = tan(a+a) = (tan(a) + tan(a))/(1 - tan(a)*tan(a) )= 2tanα/[1 - (tanα)^2] . 本文来源:https://www.wddqw.com/doc/f66bbb796beae009581b6bd97f1922791688bef7.html