tan(a+b)=2tan[(a+b)/2]/{1-{tan[(a+b)/2]}^2}=√6/(1-6/4)=-2√6tana+tanb=tan(a+b)*(1-tanatanb)=-2√6*(1-13/7)=(12√6)/7(tana-tanb)^2=(tana+tanb)^2-4tanatanb=864/49-52/7=500/49tan(a-b)=(tana-tanb)/(1+tan...1+[tan(a-b)]^2=1/[cos(a-b)]^2是怎么得到的？这是个公式我帮你证一下cos(a-b)^2=cos(a-b)^2/[cos(a-b)^2+sin(a-b)^2]=1/[1+tan(a-b)^2]就得到 1+[tan(a-b)]^2=1/[cos(a-b)]^2