COS(75度+X)=1/3,COS(150度-X)=?
问题描述：
COS(75度+X)=1/3,COS(150度-X)=?
答
cos(75°+X)=1/3,sin(75°+X)=2√2/3或-2√2/3cos(150°-X)=-cos(180°-150°+x）=-cos（30°+x）=-cos（75°+x-45°）=-cos(75°+X)cos45°-sin(75°+X)sin45°=-1/3*√2/2-(±2√2/3*√2/2)=-√2/6-(±2/3)...