sinα+cosα
=[2sin(α/2)cos(α/2)+cos^2(α/2)-sin^2(α/2)]/[sin^2(α/2)+cos^2(α/2)]
=[2tan(α/2)+1-tan^2(α/2)]/[1+tan^2(α/2)]
=1/5,
∴tan(α/2)=2或-1/3,
∴tanα
=2tan(α/2)/[1+tan^2(α/2)]
=4/5或-3/5.