由sin2α=2sinαcosα可得,（sinπ/24)(cosπ/24)=1/2*sinπ/12,
所以（sinπ/24)(cosπ/24)(cosπ/12) =1/2*（sinπ/12）*(cosπ/12)
=1/2*[1/2*sinπ/6]
=1/2*1/2*1/2
=1/8