已知tan(π/4+α)=1/2,求(sin2α-cos平方α)/(1+cos2α)的值

tan(α+π/4)=[tanα+tan(π/4)]/[1-tanαtan(π/4)]=[tanα+1]/[1-tanα][tanα+1]/[1-tanα]=1/21-tanα=2(tanα+1)3tanα=-1tanα=-1/3(sin2α-cos^2α)/(1+cos2α)=(2sinαcosα-cos^2α)/(1+2cos^2α-1)=(2sin...