题目错了吧,应该是证明(a^2-c^2)/b^2=sin(A-C)/sinB
左=(sin^2A-sin^2C)/sin^2B=(1/2)(cos(2C)-cos(2A))/sin^2B
=-sin(C+A)sin(C-A)/sin^2B
=-sin(C-A)/sinB
=sin(A-C)/sinB
=右边