求值：⑴sin(-19π/3)*cos(19π/6)

sin(-19π/3)*cos(19π/6)
=-sin(19π/3)*cos(19π/6)
=-sin(6π+π/3)*cos(3π+π/6)
=-sin(π/3)*(-cosπ/6)
=√3/2*√3/2
=3/4
cos(-585°)/[sin(-330°)+tan495°]
=cos(-585°+720°)/[sin(-330°+360°)+tan(495°-540°)]
=cos(135°)/[sin(30°)+(tan-45°)]
=-cos(135°-180°)/[sin(30°)-(tan45°)]
=-√2/2*/[1/2-1]
=√2
log2sina=-1
sina=2^(-1)=1/2
又a∈[0,2π）
a=π/6 或 5π/6