Question

若a+b=135° (1-tana)(1-tanb)的值

Answer 1

令k=(1-tana)(1-tanb)=tanatanb -tana-tanb +1,

tan(a+b)=(tana+tanb)/(1-tanatanb)=-1,

tana+tanb=-1+tanatanb,

tanatanb-tana-tanb-1=k-2=0,

则k=2