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sin36°sin54°是什么意思

积化和差公式:sin(a)sin(b) = -1/2*[cos(a+b)-cos(a-b)] 你的问题是求两个正弦函数的积,这两个角度相加为90度,所以可以使用积化和差的公式进行计算,转换为特殊角计算。

用sin2A=2sinAcosA 拼凑即得答案

sin54°cos36°+cos54°sin36° =sin(54°+36°) =sin90° =1

sin12°sin48°sin54° =(1/2)(cos36°-cos60°)cos36° =(1/2)[(cos36°)^2-(1/2)cos36°] =(1/4)[1+cos72°-cos36°] =(1/4)[1-2sin54°sin18°] =(1/4)[1-2sin54°sin18°cos18°/cos18°] =(1/4)[1-cos36°sin36°/cos18°] =(1/4)[1-sin72°/(2cos18°)] =(1/...

sin12°sin48°sin54° =(1/2)(cos36°-cos60°)cos36° =(1/2)[(cos36°)^2-(1/2)cos36°] =(1/4)[1+cos72°-cos36°] =(1/4)[1-2sin54°sin18°] =(1/4)[1-2sin54°sin18°cos18°/cos18°] =(1/4)[1-cos36°sin36°/cos18°] =(1/4)[1-sin72°/(2cos18°)] =(1/...

解: sin54°cos72° =cos36°sin18° =cos36°sin18°cos18°/cos18° =cos36°×1/2sin36°/cos18° =1/4sin72°/cos18° =1/4

sin36°=cos54° tan81°=cot9° 所以原题=cos^254°+sin^254°-cot^9°=1-cot^29°

(sin36°+sin15°sin39°)/(cos36°-cos15°sin39°) =[sin36°+(cos24°-cos54°)/2]/[cos36°-(sin54°+sin24°)/2] =(2sin36°+cos24°-sin36°)/(2sin54°-sin54°-sin24°) =(sin36°+cos24°)/(sin54°-sin24°) =(sin36°+sin66°)/(sin54°-sin24°) =(2sin51°cos1...

A、B到AO的距离是指BO的长,∵AB ∥ OC,∴∠BAO=∠AOC=36°,∵在Rt△BOA中,∠BOA=90°,AB=1,∴sin36°= BO AB ,∴BO=ABsin36°=sin36°,故本选项错误;B、由以上可知,选项错误;C、过A作AD⊥OC于D,则AD的长是点A到OC的距离,∵∠BAO=36°,∠AOB=90°,∴∠AB...

求值cos75°; cos75°=cos45°cos30°-sin45°sin30°=(√6-√2)/4 求值cos195°; cos195°=-cos15°=-(cos45°cos30°+sin45°sin30°)=-(√6+√2)/4 cos54°cos36°-sin54°sin36° =cos90°=0

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