tana=1
cosa=√2/2,sina=√2/2 或 cosa=-√2/2,sina=-√2/2
cos2a=0,sin2a=1 cos2a=0,sin2a=1
3sin(a+b)=sin(2a+b)
(3√2/2)(sinb+cosb)=cosb
3√2sinb=(2-3√2)cosb
tanb=(2-3√2)/3√2=√2/3-1
tan(a+b)=(tana+tanb)/(1-tanatanb)=(√2/3)/(1-(√2/3-1))=√2/(6-√2)