解:∵sin36°=cos54°
即sin(2×18°)=cos(3×18°)
2sin18°cos18°=4(cos18°)^3-3cos18°
∵cos18°≠0
∴2sin18°=4(cos18°)^2-3
整理得4(sin18°)^2+2sin18°-1=0
解得sin18°=(根号5-1)/4
解:∵sin36°=cos54°
即sin(2×18°)=cos(3×18°)
2sin18°cos18°=4(cos18°)^3-3cos18°
∵cos18°≠0
∴2sin18°=4(cos18°)^2-3
整理得4(sin18°)^2+2sin18°-1=0
解得sin18°=(根号5-1)/4
sin18度=(根号5-1)/4
cos18度=(根号(10+2根号5))/4
tan18度=根号((5-2根号5)/5)
cot18度=根号(5+2根号5)
sec18度=根号((10-2根号5)/5)
csc18度=根号5+1
sin18度=(根号5-1)/4
cos18度=(根号(10+2根号5))/4
tan18度=根号((5-2根号5)/5)
cot18度=根号(5+2根号5)
sec18度=根号((10-2根号5)/5)
csc18度=根号5+1
sin18=(根号5-1)/4
标签:sin18,行内,三角