1) 周长是 2派×R×54/360 + 2R
面积是 2派×R×R×54/360
2)有两总情况
3)sin25/6π+cos25/3π+tan(-25/4π)
=sin1/6π+cos2/3π - tan(1/4π)
=1/2 - 1/2 - 1
=-1
4)sin(π+α)= -1/2 sinα = 1/2
cos = 根3/2 cos = - 根3/2
5)cos2x = 2tanx/(1-tanx*tanx)
1) 周长是 2派×R×54/360 + 2R
面积是 2派×R×R×54/360
2)有两总情况
3)sin25/6π+cos25/3π+tan(-25/4π)
=sin1/6π+cos2/3π - tan(1/4π)
=1/2 - 1/2 - 1
=-1
4)sin(π+α)= -1/2 sinα = 1/2
cos = 根3/2 cos = - 根3/2
5)cos2x = 2tanx/(1-tanx*tanx)