sin4/3π乘以cos19/6π乘以tan21/4π
=sin(π+π/3)*cos(3π+π/6)*tan(5π+π/4)
=-sin(π/3)*cos(π+π/6)*tan(π/4)
=-(根号3)/2*[-cos(π/6)]*1
=(根号3)/2*(根号3)/2
=3/4