sina=2根号5 5,sin(a b-搜答案-搜狗做题网

sina+根号3cosa=2[(1/2)sina+(根号3/2)cosa]=2sin(a+60度)

sin(a+π/3)+sina=(-4/5)*根号3展开左边,即√3sin(a+π/6)=(-4/5)*根号3∴sin(a+π/6）=-4/5∵-π/2再问：麻烦下左边的式子怎么拆开请帮下。。怎么得到

两边平方得1-2sina*cosa=3/2,整理得sina*cosa=-1/4

cos2a/sin(a-pai/4)=-根号2／2cos2a/(sinacos(pai/4)-cosasin(pai/4))=-根号2／2cos2a/(根号2／2*sina-根号2／2*cosa)=-

sin(a+π/3）+sina=1/2sina+√3/2cosa+sina=3/2sina+√3/2cosa=√3（√3/2sina+1/2cosa)=√3cos(a-π/3）=-√3cos(a+2π

sin(a-π/4)/cos2a=[(√2/2)(sina-cosa)]/(cos²a-sin²a)={(√2/2)(sina-cosa)}/{(cosa+sina)(cosa-s

sin(a+π/3)+sina=sinacos(π/3)+sin(π/3)cosa+sina=-4√3/5化简得到√3sina+cosa=-8/5再利用sina^2+cosa^2=1带入解得cosa再

cos2a=(cosa)^2-(sina)^2sin(a-45°)=√2/2(sina-cosa)∴cos2a/sin(a-45°)=-√2(sina+cosa)=-√2/2∴cosa+sina=1/

(sina-cosa)²=sin²a+cos²a-2sinacosa=1-2sinacosa=2/252sinacosa=23/25(sina+cosa)²=1

∵sin(a+π/3)+sina=-4根号3/5∴sina/2+(cosa根号3)/2+sina=（-4根号3）/5∴（（sina*根号3）/2+cosa/2）*根号3=（-4根号3）/5∴sin（a

cosa+cosβ=ksina+sinβ=根号2/2sina+sinβ+cosa+cosβ=根号2/2+k根号2sin(a+π/4)+根号2sin(β+π/4)=根号2/2+k-1

sina+cosa=根号2两边平方1+2sinacosa=2sinacosa=1/2sin四次方a+cos四次方a=（sina+cosa）-2sinacosa=1-2×1/4=1/2

答案如下

(sina－cosa)²=(√2/2)²1－2sinacosa=1/22sinacosa=1/2sinacosa=1/4sin^a＋cos^4a=(sin²a＋cos&#

(3cosa－2sina)²=139cos²a－12sinacosa＋4sin²a=139cos²a－12sinacosa＋4sin²a=13sin&

sina+cosa=根号2/2sin2a,说明sin2a=1再答：2a=2kπ+π/2再答：4a=2*(2k)π+π再问：sin^4a+cos^4a=再答：-1再问：嗯

分子cos2a=cos^2a-sin^2=(cosa+sina)(cosa-sina),分母sin(a-Pi/4)=(sina-cosa)*（根号2）/2所以由题直接得,答案=1/2

cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4))/(2sin(a-π/4)cos(a-π/4))cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4))/sin