sin(A-B)/sin(A+B)=(2c-b)/(2c),∴（sinAcosB-cosAsinB)/sinC=(acosB-bcosA)/c=(2c-b)/(2c）,∴2acosB-2bcosA=2c-b,由余弦定理,（a^2+c^2-b^2)/c-(b^2+c^2-a^2)/c=2c-b,∴2a^2-2b^2=2c^2-bc,∴a^2=b^2+c^2-bc/2,观察...