根据正弦定理,a/sinA=b/sinB=c/sinC=2R
所以,sinB=b/(2R)
2R(sin^A-sin^C)=(√2a-b)*b/(2R)
4R^2(sin^A-sin^C)=(√2a-b)*b
a^2-c^2=√2ab-b^2
c^2=a^2+b^2-√2ab
根据余弦定理,c^2=a^2+b^2-2abcosC得,
cosC=√2/2 C=45