导期 解：(1)sin54°-sin18°=2c0s36°sin18° 2 2sin18°c0s18°c0s36° 2sin36°c0s36 sin72° 2c0s18° 2c0S18° 2c0s18° C0S18° 2c0s18°1 2 (2)c0s146°+c0s94°+2c0s47°c0s73° =2c0s120°c0s26°+2×(c0s120°+c0s26°) =2×(2)×c0s26°+()+c0s26° =-c0s26°+(-2)+c0s26°=2
导航 解:(1)sin 54°-sin 18°=2cos 36°sin 18° =2× 𝟐𝐬𝐢𝐧𝟏𝟖°𝐜𝐨𝐬𝟏𝟖°𝐜𝐨𝐬𝟑𝟔° 𝟐𝐜𝐨𝐬𝟏𝟖° = 𝟐𝐬𝐢𝐧𝟑𝟔°𝐜𝐨𝐬𝟑𝟔° 𝟐𝐜𝐨𝐬𝟏𝟖° = 𝐬𝐢𝐧𝟕𝟐° 𝟐𝐜𝐨𝐬𝟏𝟖° = 𝐜𝐨𝐬𝟏𝟖° 𝟐𝐜𝐨𝐬𝟏𝟖° = 𝟏 𝟐 . (2)cos 146°+cos 94°+2cos 47°cos 73° =2cos 120°cos 26°+2× 𝟏 𝟐 (cos 120°+cos 26°) =2× - 𝟏 𝟐 ×cos 26°+ - 𝟏 𝟐 +cos 26° =-cos 26°+ - 𝟏 𝟐 +cos 26°=- 𝟏 𝟐
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(4+B)-sin(A-B)=2cos Asin B.( (3)cos(A+B)+cos(4-B)=2cos Acos B.( (4)cos(4+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.( × )