第1个回答 2013-12-07
你好
1、tan2θ=2tanθ/(1-tan²θ)=-6/(-8)=3/4
2、
原式
=(2cos²θ/2-1+sinθ)/√2sin(π/4-θ)
=(cosθ+sinθ)/√2cos[π/2-(π/4-θ)]
=√2(√2/2cosθ+√2/2sinθ)/√2cos(π/4+θ)
=(sinπ/4cosθ+cosπ/4sinθ)/cos(π/4+θ)
=sin(π/4+θ)/cos(π/4+θ)
=tan(π/4+θ)
=(tanπ/4+tanθ)/(1-tanπ/4tanθ)
=(1-3)/[1-1*(-3)]
=-2/4
=-1/2