设5π设5π设5πsin(a/4)=正负(1-cos(a/2))/2因为5π所以sin(a/4)=负(1-cos(a/2))/2
设5πsin(a/4)=正负(1-cos(a/2))/2因为5π所以sin(a/4)=负(1-cos(a/2))/2