de等于4分之3bd,求sinc的值
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sina=4√3/7≈0.9897433a=arcsin0.9897433≈81.79°
36.87°,这个角度符合勾三股四弦五.
sin(4分之派-a)=sin[π-(α+π/4)]=cos(α+π/4)=2/3再问:http://zhidao.baidu.com/question/2074206122687787188.htm
因为sin(4分之π-x)等于13分之5,即sin(π/4-x)=5/13cos(x-π/4+π/2)=-sin(x-π/4)=sin(π/4-x)=5/13cos[2(x+π/4)]=-sin2x=
再答:求采纳哇亲
"sin(β加π)等于负的13分之20"有误?cos(α加β)=cosαcosβ-sinαsinβ
勾股定理:AD=√(BD^2-AB^2)=√(12^2-10^2)=2√11∵BD是角平分线∴DE=AD=2√11二倍角公式:cos∠ABC=2(cos∠DBA)^2-1=2*(10/12)^2-1=
显然角DEB=角CBE^2=DE^2+BD^2=25/16BD^2BE=5/4BDsinC=BD/BE=4/5
sin(x-4分之π)=-sin(π/4-x)=-sin[π/2-(π/4+x)]=-cos[(π/4)+x]=1/3所以:cos[(π/4)+x]=-1/3
cosθ=-12/13θ属于(π,3/2π),则sinθ=-5/13sinθ(θ+π/4)=sinθcosπ/4+cosθsinπ/4=-5/13*√2/2-12/13*√2/2=-17√2/26再问
f(5π/4)=2sin(5π/12-π/6)=2sin(3π/12)=2sin(π/4)=√2
采纳秒回再问:求san,cosA的值再答: 再答:
∵AD平行于BC,∴∠ADB=∠DBC又∵AB等于CD等于AD∴∠B=∠C=2∠DBC又∵BD垂直CD∴∠DBC﹢∠C=90°∴∠DBC=30°∴BC=2DC又∵SIN角DBC=DC∶BC∴SIN角D
=(tana+1)/(tana-1)=-2再答:=2再答:不好意思
sinα+cosα=1/2两边平方sin²α+2sinαcosα+cos²α=1/4sin²α+cos²α=1所以sinαcosα=-3/8
COSα=5分之4,tanα=负4分之3.或者cosα=负5分之4,tanα=4分之3.
AD:DC=3:1,又∵ED//BC∴ED:BC=AD:AC=3:4,∴BC=8.∵BD是∠ABC的角平分线∴根据角平分线定理有AB:BC=AD:DC=3:1,∴AB=24
sinx=3/5易知x=arcsin(3/5)