sin(派/6+2a)
=sin[2(a+派/3)-派/2]
=-cos[2(a+派/3)]
=2[sin(a+派/3)]^-1
=-1/9 sin(派/6+2a)
=sin[2(a+派/3)-派/2]
=-cos[2(a+派/3)]
=2[sin(a+派/3)]^-1
=-1/9