已知2sina cosa=1

(sinA+cosA)^2=1/4sin^2A+cos^2A+2sinAcosA=1/42sinAcosA=-3/4sinAcosA=-3/8sinAcosA/(sin^2A+cos^2A)=-3/8

tan(π/4+a)=[tanπ/4+tana)/[1-tanπ/4*tana]=2(1+tana)/(1-tana)=2tana=1/31/(2sinacosa+cos²a)=(sin&#

cosa-sina=-根号(1-2sinacosa)=-根号(1-1/4)=-√3/2答案：B-根号3/2

sinA^2+cosA^2=11/(sinA^2-sinAcosA-2cosA^2)=(sinA^2+cosA^2)/(sinA^2-sinAcosA-2cosA^2)=(tanA^2+1)/(tan

tan(a-4/π)=(tana-tanπ/4)/(1+tanatanπ/4)=(tana-1)/(1+tana)=2,所以tana=-3而1/(2sinacosa+cos^2a)=(sin^2a+c

tana＝sina/cosa＝1/2,所以cosa＝2sina,所以根据sin^2a＋cos^2a＝1,求出sin,cos

tana=2/3万能公式sin2a＝2tana/(1+tan^2a)1/sinacosa=2/2sinacosa=2/sin2a=2(1+tan^2a)/2tana=(1+tan^2a)/tana=(

tana/（tana-1）=-1,tana=1/2sin²a+sinacosa+2=(sin²a+sinacosa)/1+2=(sin²a+sinacosa)/(sin^

sin²a+sinacosa+2=（sin²a+sinacosa）/(sin²a+cos²a)+2=(tan²a+tana)/(tan²a+

tana=根号2;sin²a=4/5,cos²a=1/52sin²a-sinacosa+cos²a-1=sin²a-sinacosa=sin²

2sin²a+2sinacosa/1+tana=2sina(sina+cosa)/[(sina+cosa)/cosa]=2sinacosak=2sinacosa(sina-cosa)^2=1

tanA=2运用公式sin2A=2tanA/(1+tan^2A)=4/5sin^2A=tan^2A/(1+tan^2A)=4/5则sinAcosA=sin2A/2=2/5(sinAcosA-sin^2

tanA=-1/21+(2sinAcosA)/(sinA-cosA)=(sinA-cosA+2sinAcosA)/(sinA-cosA)分子分母同除以一个cosA→(tanA-1+2tanA)/tan

sinacosa=1/8所以sina,cosa>0又因为（sina）²+（cosa）²=1所以（sina）²+（cosa）²+2sinacosa=1+1/4（s

用万能公式,cos2A=sin(π/2+2A)=2tan[(π/4)+A]/{1+tan^2[(π/4)+A]}=4/5sin2A=-cos[(π/2)+2A]=-{1-tan^2[(π/4)+A]}

cosa=3/2sina原式=sina^2-2sina*3/2sina+9/4sina^2=1/4sina^2又cosa^2+sina^2=1得sina^2=4/13则原式=1/13

1-cos2a/sinacosa=1-2(cos2a/2sinacosa)=1-2(cos2a/sin2a)=1-2cot2atana=0.5,tan2a=2tana/(1-tana*tana)=4/

tana\tana-1=-1,tana=1/2,2sina=cosa,4sin²a=1-sin²a,sin²a=1/5,cos²a=4/5,2sinacosa=

sin^2a+sinacosa/sin^2+1?是sin^2a+sinacosa/sin^2a+1吧?sin^2a+sinacosa/sin^2a+1=sin^2a+sinacosa/（2sin^2a