最终结果等于1.
(3a-6b)/(a+b) - (4a-5b)/(a+b) - (5a-6b)/(a-b) - (7a-8b)/(b-a)
=(3a-6b-4a+5b)/(a+b)- (5a-6b)/(a-b)+ (7a-8b)/(a-b)
=(-a-b)/(a+b)+(7a-8b-5a+6b)/(a-b)
=-1+2=1