tana=1/7,tanb=1/3tan(a+b)=(tana+tanb)/(1-tanatanb)=(1/7+1/3)/(1-1/21)=1/2.tan(a+b+b)=[tan(a+b)+tanb]/[1-tan(a+b)tanb]=(1/2+1/3)/(1-1/2*1/3)=1因为:0<β<π/2 ,所以:0<2β<π (α值的范围不知)α+2β=π/4或者α+2β=5π/4.