(a-2b+3c)/(a+b-c)-(a-b+c)/(a-c+b)+(2c-d)/(c-a-b)
=(a-2b+3c)/(a+b-c)-(a+b-c)/(a+b-c)-(2c-d)/(a+b-c)
=(a-2b+3c-a+b-c-2c+d)/(a+b-c)
=(-b+d)/(a+b-c).