第1个回答 2010-07-19
1)
sin3A/sinA=(sin2AcosA+cos2AsinA)/(sin2AcosA-cos2AsinA)=13/5
5sin2A+5cos2AsinA=13sin2AcosA-13cos2AsinA
8*2sinAcosA*cosA=18cos2AsinA
8cosA*cosA=9cosA*cosA-9sinA*sinA
tanA=-1/3或者1/3
tan2A=2tan2A/(1-tanA*tanA)=-3/4 或者3/4
2)(sinA+cosA)^2=1+sin2A=5/3
sinA>0 cosA>0
sinA+cosA=(根号15)/3
3)tana- 1/tana=-4
sina/cosa -cosa/sina=(sin^2a-cos^2a)/(sinacosa)=-2cos2a/sin2a=-4
cos2a/sin2a=2 tan2a=1/2
tan(π/4+2a)=tanπ/4 +tan2a/[1-tanπ/4 tan2a]=(1+tan2a)/[1-tan2a]
=3/2 ÷1/2=3本回答被提问者采纳