sin2(α)+cos2(α)=1sin2(α)+cos2(α)=1
在单位圆中,sin(α)sin(α)与cos(α)cos(α)为直角边,斜边为1,利用勾股定理即可。
sin(α+β)=sin(α)cos(β)+cos(α)sin(β)sin(α+β)=sin(α)cos(β)+cos(α)sin(β)
cos(α+β)=cos(α)cos(β)−sin(α)sin(β)cos(α+β)=cos(α)cos(β)−sin(α)sin(β)
tan(α+β)=tan(α)+tan(β)1−tan(α)tan(β)tan(α+β)=tan(α)+tan(β)1−tan(α)tan(β)
sin(α−β)=sin(α)cos(β)−cos(α)sin(β)sin(α−β)=sin(α)cos(β)−cos(α)sin(β)
cos(α−β)=cos(α)cos(β)+sin(α)sin(β)cos(α−β)=cos(α)cos(β)+sin(α)sin(β)
tan(α−β)=tan(α)−tan(β)1+tan(α)tan(β)
sin(α)+sin(β)=2sin(α+β2)cos(α−β2)sin(α)+sin(β)=2sin(α+β2)cos(α−β2)
sin(α)−sin(β)=2cos(α+β2)sin(α−β2)sin(α)−sin(β)=2cos(α+β2)sin(α−β2)
cos(α)+cos(β)=2cos(α+β2)cos(α−β2)cos(α)+cos(β)=2cos(α+β2)cos(α−β2)
cos(α)−cos(β)=2sin(α+β2)sin(α−β2)cos(α)−cos(β)=2sin(α+β2)sin(α−β2)
tan(α)+tan(β)=sin(α+β)cos(α)cos(β)tan(α)+tan(β)=sin(α+β)cos(α)cos(β)
tan(α)−tan(β)=sin(α−β)cos(α)cos(β)
sin(2α)=2sin(α)cos(α)sin(2α)=2sin(α)cos(α)
cos(2α)=cos2(α)−sin2(α)cos(2α)=cos2(α)−sin2(α)
tan(2α)=2tan(α)1−tan2(α)tan(2α)=2tan(α)1−tan2(α)