二倍角与半角的余弦正弦和正切(共15页).doc

精选优质文档-倾情为你奉上55二倍角与半角的正弦、余弦和正切基本公式sin(+)=sincos+cossinsin2=2sincos（S2）;cos(+)=coscos-sinsincos2=cos2-sin2(C2);tan(+)= 因为，所以公式可以变形为或 变形公式，统称为二倍角的三角函数公式，简称为二倍角公式*积化和差公式的推导 sin(a + b) + sin(a - b) = 2sinacosb sinacosb =sin(a + b) + sin(a - b)sin(a + b) - sin(a - b) = 2cosasinb cosasinb =sin(a + b) - sin(a - b)cos(a + b) + cos(a - b) = 2cosacosb cosacosb =cos(a + b) + cos(a - b)cos(a + b) - cos(a - b) = - 2sinasinb sinas