cos36-cos72
=cos(54-18)-cos(54+18)
=cos54cos18+sin54sin18-[cos54cos18-sin54sin18]
=2sin54sin18
=-2sin54sin(-18)
=2sin54sin18
=2cos36sin18
=2cos36sin18cos18/cos18
=cos36sin36/cos18
=sin72/(2cos18)
=sin72/(2sin72)=1/2
cos36°-cos72°=?cos36-cos72=-2sin54sin(-18)这一步看不懂=2sin54sin18
3个回答
相关问题
-
sin54°cos36°+cos54°sin36°
-
sin72°,cos72°,sin36°,cos36°分别等于多少?
-
cos36 sin36 tan36 cos72 sin72 tan72 等于多少?
-
((cos54)^2-3(sin54)^2)((cos18)^2-3(sin18)^2)=-1
-
求值cos75°;求值cos195°;cos54°cos36°-sin54°sin36°
-
sin72度cos18度+cos72度+sin18度 急
-
(1)Sin72度Cos18度 Cos72度Sin18度=?
-
(1)Sin72度Cos18度 Cos72度Sin18度=?
-
sin72°cos27°-sin18°sin27°
-
sin36=cos72吗?