sin(a-π/4）=7√2/10
sinacosπ/4-sinπ/4cosa=7√2/10
sina-cosa=7/5 (1)
cos2a=7/25
cos²a-sin²a=7/25
(cosa+sina)(cosa-sina)=7/25
sina+cosa=-1/5 (2)
(1)+(2)得2sina=6/5
sina=3/5
(1)-(2)得2cosa=8/5
cosa=4/5
∴tana=3/4
tan(a+π/3）=(tana+tanπ/3)/(1-tanatanπ/3)
=-(48+25√3)/11