导航 解：(1)sin54°-sin18°=2cos36°sin18° 2 2sin18°cos18°c0s36° 2sin36°c0s36° sin72 2c0s18° 2c0s18° 2c0s18° c0s18° 2c0s18°1 2 (2)c0s146°+c0s94°+2c0s47°c0s73° =2c0s120°c0s26°+2x×(c0s120°+c0s26°) =2×(2)×c0s26°+()+c0s26 =c0s26°+(-2)+c0s26°=2
导航
导 【思考辨析】 判断下列说法是否正确，正确的在它后面的括号里画“√”，错 误的画“X”. (1)sin(A+B)+sin(A-B)=2sin Acos B.( (2)sin(A+B)-sin(A-B)=2cos Asin B.( (3)cos(4+B)+cos(A-B)=2cos Acos B.( (4)cos(A+B)-cos(A-B)=2cos Acos B.(
导航 【思考辨析】 判断下列说法是否正确,正确的在它后面的括号里画“√” ,错 误的画“×” . (1)sin(A+B)+sin(A-B)=2sin Acos B.( √ ) (2)sin(A+B)-sin(A-B)=2cos Asin B.( √ ) (3)cos(A+B)+cos(A-B)=2cos Acos B.( √ ) (4)cos(A+B)-cos(A-B)=2cos Acos B.( × )