sin(990°+α)化成角α的三角函数

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sin(990°+α)化成角α的三角函数

sin(990°+α)化成角α的三角函数
sin(990°+α)化成角α的三角函数

sin(990°+α)化成角α的三角函数
sin(990°+α)
=sin(360ºx3-90°+α)
=sin(-90°+α)
=-sin(90°-α)
=-cosα

sin(990°+a)=sin(360°×2+270°+a)=sin(270°+a)=sin(a-90°)=-sin(90°-a)=-cosa

sin(990°+α)
=sin(1080°-90°+α)
=sin(-90°+α)
=cos(180°-α)
=-cosα