1.cos2a/sin(a-π/4)=-√2/2,那么sina+cosa的值为?2.在三角形ABC中,tanA=1/2,cosB=3√10/10,则tanC的值是?3.要使得sina-√3cosa9=(4m-6)/(4-m)有意义,则m的取值范围是?
来源:学生作业学帮网 编辑:学帮网 时间:2024/05/14 10:21:16
1.cos2a/sin(a-π/4)=-√2/2,那么sina+cosa的值为?2.在三角形ABC中,tanA=1/2,cosB=3√10/10,则tanC的值是?3.要使得sina-√3cosa9=(4m-6)/(4-m)有意义,则m的取值范围是?
1. cos2a/sin(a-π/4)=-√2/2,那么sina+cosa的值为?
cos2a=(-√2/2)(sinacosπ/4-cosasinπ/4)=(-sina-cosa)/2
cos2a=cos^2a-sin^2a=(-sina-cosa)/2
cos^2a-cosa/2=sin^2a-sina/2
(cosa-1/4)^2=(sina-1/4)^2
所以cosa=sina=√2/2,cosa+sina=√2或cosa-1/4=1/4-sina,cosa+sina=1/2
2.在三角形ABC中,tanA=1/2,cosB=3√10/10,则tanC的值是?
tanA=1/2,2sinA=cosA,4sin^2A=cos^2A,sinA=√5/5,cosA=2√5/5
cosB=3√10/10,sinB=√10/10
sinC=sin(B+A)=sinBcosA+sinAcosB=√2/2
cosC=-cos(B+A)=-(cosBcosA-sinBsinA)=-√2/2
tanC=-1
3. 要使得sina-√3cosa9=(4m-6)/(4-m)有意义,则m的取值范围是?
sina-√3cosa9?sina-√3cosa?
-2
证明:2sin(π/4+a)sin(π/4-a)=cos2a
求证:2sin(π/4+a)sin(π/4-a)=cos2a
sin(π/4+a)sin(π/4-a)=1/6求cos2a
tan(a+π/4)=2,则cos2a+3sin^2a+tan a=
已知sin(a-π)=3/5,求cos2a
sin(a-π)=3/5求cos2a的值
已知cos2a=1/4,则sin^2 a=?
已知cos2a=1/4,则sin^2 a=
已知sin(π/4+a)+cos(π/4-a)=1/5,则cos2a
已知cos2a=4/5,且a属于[2分之π,π],则sin a=?
a属于(0,π/2),sin^2a+cos2a=1/4,则tana=
a是第四象限的角,cosa=5/13,sin(a+π/4)/cos2a=?
tan(a+π/4)=2,则cos2a+3sin^2a+tan2a=
已知tan(a+π/4)=2 求cos2a+3sin²a得值
已知tan(a+π/4)=2,求cos2a+3sin²a的值
若cos2a/sin(a-π/4)=-根号2/2 求:1.cosa+sina;2.cosa-sina; 3.tana
若sin(a-π/4)/cos2a=-根号2,则sina+cosa=
cos2a/sin(a-π/4) =-根号(2)/2,则cosa+sina的值为?