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=-(cos5cos25-sin5sin25) =-cos30 =-√3/2 ?

因为:cos(a+b)=(cosacosb-sinasinb) 所以:-cos(a+b)=-(cosacosb-sinasinb) 这里的a=5,b=25 所以: -(cos5cos25-sin5sin25) =-cos(5+25) =-cos30 =-√3/2 很高兴为您解答,祝你学习进步! 如果我的回答对你有帮助,请及时选为满意答...

(cos85°+sin25°cos30°)/cos25° = {cos(60°+ 25°) + sin25°cos30°} /cos25° = {cos60°cos25° - sin60°sin25° + sin25°cos30°} /cos25° = {cos60°cos25° - sin25°(sin60° - cos30°) } /cos25° = cos60°cos25° / cos25° = cos60° = 1/2

A、cos215°-sin215°=cos2×15°=cos30°=32,不合题意;B、sin45°cos15°+cos45°sin15°=sin(45°+15°)=sin60°=32,不合题意;C、cos25°cos5°+sin25°sin5°=cos(25°-5°)=cos20°≠32,符号题意;D、cos25°cos5°-sin25°sin5°=cos(25°+5°)=cos30°=32...

sin(25*3.14/180)+cos(30*3.14/180)

(cos85°+sin25°cos30°)/cos25° = {cos(60°+ 25°) + sin25°cos30°} /cos25 ° = {cos60°cos25° - sin60°sin25° + sin25...

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