作业帮求值：⑴sin(-19π/3)*cos(19π/6)⑵cos(-585°)/[sin(-330°)+tan495°]已知log2sina=-1且a∈[0,2π）,求a的值
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![求值：⑴sin(-19π/3)*cos(19π/6)⑵cos(-585°)/[sin(-330°)+tan495°]已知log2sina=-1且a∈[0,2π）,求a的值](/uploads/image/z/5917266-18-6.jpg?t=%E6%B1%82%E5%80%BC%EF%BC%9A%E2%91%B4sin%28-19%CF%80%2F3%29%2Acos%2819%CF%80%2F6%29%E2%91%B5cos%28-585%C2%B0%29%2F%5Bsin%28-330%C2%B0%29%2Btan495%C2%B0%5D%E5%B7%B2%E7%9F%A5log2sina%3D-1%E4%B8%94a%E2%88%88%5B0%2C2%CF%80%EF%BC%89%2C%E6%B1%82a%E7%9A%84%E5%80%BC)
求值：⑴sin(-19π/3)*cos(19π/6)⑵cos(-585°)/[sin(-330°)+tan495°]已知log2sina=-1且a∈[0,2π）,求a的值
求值：⑴sin(-19π/3)*cos(19π/6)
⑵cos(-585°)/[sin(-330°)+tan495°]
已知log2sina=-1且a∈[0,2π）,求a的值
求值：⑴sin(-19π/3)*cos(19π/6)⑵cos(-585°)/[sin(-330°)+tan495°]已知log2sina=-1且a∈[0,2π）,求a的值
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