求值:sin21°cos81°-sin69°cos9°=______.
题型:填空题难度:一般来源:不详
求值:sin21°cos81°-sin69°cos9°=______. |
答案
sin21°cos81°-sin69°cos9°=sin21°cos(90°-9°)-sin(90°-21°)cos9° =sin21°sin9°-cos21°cos9°=-(cos21°cos9°-sin21°sin9°)=-cos(21°+9°)=-cos30°=- 故答案为:- |
举一反三
若α∈(0,),则点P(sin(+α),cos(-α))在第______象限. |
sin2(π+α)-cos(π+α)•cos(-α)+1的值为 ______. |
若=2,则sin(θ-5π)•sin(-θ)=______. |
化简: (1)sin[α+(2n+1)π]+sin[α-(2n+1)π] | sin(α+2nπ)•cos(α-2nπ) |
(2)1-cos4α-sin4α | 1-cos6α-sin6α | . |
已知cos2α=(其中α∈(-,0)),则sinα的值为 ______. |
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