7x^2-8x+1=0(7x-1)(x-1)=0x1=1/7,x2=1所以设tana=1,tanb=1/7.或者由韦达定理得tana+tanb=8/7,tanatanb=1/7tan(a+b)=(tana+tanb)/(1-tanatanb)=(8/7)/(1-1/7)=4/3.tan(a+b)=2[tan(a+b)/2]/[1-(tan(a+b)/2)^2]设tan(a+...