tanB=1/4,tanC=3/5
tan(B+C)= ( tanB+tanC)/(1-tanA*tanB)
= [(1/4)+(3/5)] / [1-(1/4)*(3/5)]
= 1
tanA=-tan(B+C)=-1
A=135度
角A最大,所以a=√17,角B最小,b边最短
sinB=1/√5 sinA=√2/2
b=a/sinA*sinB
=√17/(√2/2)*(1/√5)
=√170 /5sinB怎么算的？tanB=1/4x=4t ,y=1t ,r=√5 ttanB=y/xsinB=y/r=1/√5r我算出来是√17。。哦，你是对的sinB=1/√17b=a/sinA*sinB=√17/(√2/2)*(1/√17)=√2