tanα=1/3,且sin^2(α)+cos^2(α)=1原式=(2cos^2(α)+2sinαcosα)/(sin^2(α)+cos^2(α))分号上下同除以cos^2(α),=(2+2tanα)/(tan^2(α)+1)将tanα=1/3代入,得 =(2+2/3)/(1/9+1)=(8/3)/(10/9)=12/5
