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Cos75度

sin75°=sin(45°+30°)=sin45°cos30°+cos45°sin30°=(√6+√2)/4 cos75=cos(30+45)=cos30cos45-sin30sin45=√6/4-√2/4=(√6-√2)/4

cos(75)=cos(45+30) =cos45cos30-sin45sin30 =√2/2 *√3/2- √2/2*1/2 =(√6-√2)/4

cos75-cos15 =cos(45+30)-cos(45-30) =cos45cos30-sin45sin30-(cos45cos30+sin45sin30) =cos45cos30-sin45sin30-cos45cos30-sin45sin30 =-2sin45sin30 =-2*(√2)/2*1/2 =-(√2)/2

cos75=0.259 或者 cos75=cos(30+45)=cos30cos45-sin30sin45=√6/4-√2/4=(√6-√2)/4

cos平方75°+cos平方15°+cos15°乘cos75° =sin²15°+cos²15°+cos75°cos15° =1+cos75°cos15° =1+sin15°cos15° =1+(2sin15°cos15°)/2 =1+sin30°/2 =1+1/4 =5/4

等于。

sin15°=cos75°=(√6-√2)/4 cos15°=sin75°=(√6+√2)/4 tan15°=cot75°=(√6-√2)/(√6+√2)=(√6-√2)^2/4=2-√3 tan75°=cot15°=(√6+√2)/(√6-√2)=(√6+√2)^2/4=2+√3

cos^2(15°)+cos^2(75°)+sin15°*sin75° =cos^2(15°)+sin^2(15°)+sin15°cos15° =1+sin30°/2 =1+1/4 =5/4 希望对你有所帮助 还望采纳~~

变成sin(45+30)展开算

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