求证题能不能写详细点要步骤.急!（cos^2a-sin^2a)/sinacosa=2ctg2a、ctga-tga=2ctg2a、(1+sin2a-cos2a)/(1+sin2a+cos2a)=tga、2sin^2(a/2)+cosa=1

求证题能不能写详细点要步骤.急!（cos^2a-sin^2a)/sinacosa=2ctg2a、ctga-tga=2ctg2a、(1+sin2a-cos2a)/(1+sin2a+cos2a)=tga、2sin^2(a/2)+cosa=1
求证题能不能写详细点要步骤.急!
（cos^2a-sin^2a)/sinacosa=2ctg2a、ctga-tga=2ctg2a、(1+sin2a-cos2a)/(1+sin2a+cos2a)=tga、2sin^2(a/2)+cosa=1

求证题能不能写详细点要步骤.急!（cos^2a-sin^2a)/sinacosa=2ctg2a、ctga-tga=2ctg2a、(1+sin2a-cos2a)/(1+sin2a+cos2a)=tga、2sin^2(a/2)+cosa=1
1、(cos^2a-sin^2a)/sinacosa=2ctg2a
因为,cos^2a-sin^2a=cos2a,sinacosa=sin2a/2
所以,(cos^2a-sin^2a)/sinacosa=cos2a/sin2a/2=2cos2a/sin2a=2ctg2a
2、ctga-tga=2ctg2a
ctga-tga=(cosa/sina)-(sina/cosa)=(cos^2a-sin^2a)/sinacosa=2ctg2a
3、(1+sin2a-cos2a)/(1+sin2a+cos2a)=tga
(1+sin2a-cos2a)/(1+sin2a+cos2a)=(cos^2a+sin^2a+2sinacosa-cos^2a+sin^2a)/(cos^2a+sin^2a+2sinacosa+cos^2a-sin^2a)=(2sin^2a+2sinacosa)/(2sinacosa+2cos^2a)=2sina(sina+cosa)/2cosa(sina+cosa)=sina/cosa=tga
4、2sin^2(a/2)+cosa=1
因为cosa=cos^2(a/2)-sin^2(a/2)
所以2sin^2(a/2)+cosa=2sin^2(a/2)+cos^2(a/2)-sin^2(a/2)=sin^2(a/2)+cos^2(a/2)=1

1.（cos^2a-sin^2a)/sinacosa=2（cos(2a))/2sinacosa=2cos(2a)/sin(2a)=2ctg(2a)
2.ctg(a)-tg(a)=cosa/sina-sina/cosa=(cos^2a-sin^2a)/sinacosa=2（cos(2a))/2sinacosa=2cos(2a)/sin(2a)=2ctg(2a)
3.(1+sin2a-...

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1.（cos^2a-sin^2a)/sinacosa=2（cos(2a))/2sinacosa=2cos(2a)/sin(2a)=2ctg(2a)
2.ctg(a)-tg(a)=cosa/sina-sina/cosa=(cos^2a-sin^2a)/sinacosa=2（cos(2a))/2sinacosa=2cos(2a)/sin(2a)=2ctg(2a)
3.(1+sin2a-cos2a)/(1+sin2a+cos2a)=(2sin^2a+2sinacosa)/(2cos^2a+2sinacosa)=sina(sina+cosa)/cosa(sina+cosa)=sina/cosa=tga
4.2sin^2(a/2)+cosa=2sin^2(a/2)-1+cosa+1=-cosa+cosa+1=1

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(cos^2a-sin^2a)/sinacosa=[(cos(2a)+1)/2-(1-cos(2a))/2]/[sin(2a)/2]=2cos(2a)/sin(2a)=2ctg(2a)
ctga-tga=cosa/sina-sina/cosa=(cos^2a-sin^2a)/sinacosa=2ctg2a
(1+sin2a-cos2a)/(1+sin2a+cos2a)=[1+2si...

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(cos^2a-sin^2a)/sinacosa=[(cos(2a)+1)/2-(1-cos(2a))/2]/[sin(2a)/2]=2cos(2a)/sin(2a)=2ctg(2a)
ctga-tga=cosa/sina-sina/cosa=(cos^2a-sin^2a)/sinacosa=2ctg2a
(1+sin2a-cos2a)/(1+sin2a+cos2a)=[1+2sinacosa-(2cos^2a-1)]/[1+2sinacosa+(2cos^2a-1)]=
(sinacosa+sin^2a)/(sinacosa+cos^2a)=sina/cosa=tga
2sin^2(a/2)+cosa=1-cosa+cosa=1

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这是几个题啊？看不懂