sinb=(根号10/10）,ab是锐角,则有cosb=√(1-sin^2b)=3√10/10,tanb=sinb/cosb=1/3.tan2b=2tanb/(1-tan^2b)=3/4.tan（a+2b）=(tana+tan2b)/(1-tana*tan2b)=(1/7+3/4)/(1-1/7*3/4)=25/25=1.