(1)a/sinA=b/sinB=C/sinC=k
a=ksinA
b=ksinB
c=ksinC
(2a-c)/b=(2ksinA-ksinC)/ksinB
=(2sinA-sinC)/sinB
(2a-c)cosB=bcosC可化为
(2sinA-sinC)cosB=sinBcosC
2sinAcosB=sin(B+C)=sinA
2cosB=1
cosB=1/2
B=60°
(2)题目目不全
(1)a/sinA=b/sinB=C/sinC=k
a=ksinA
b=ksinB
c=ksinC
(2a-c)/b=(2ksinA-ksinC)/ksinB
=(2sinA-sinC)/sinB
(2a-c)cosB=bcosC可化为
(2sinA-sinC)cosB=sinBcosC
2sinAcosB=sin(B+C)=sinA
2cosB=1
cosB=1/2
B=60°
(2)题目目不全