tan(a+π/4)=1(tana+tanπ/4)/(1-tanatanπ/4)=1(tana+1)/(1-tana)=1tana+1=1-tanatana=0(sin2a-cosa^2)/(1+cos2a)=(2sinacosa-cosa^2)/2cosa^2=(2sina-cosa)/2cosa=2tana-1/2=-1/2