楼上错了
a平方+b平方/2ab=2
a²+b²=4ab
7ab/a平方+b平方+3a平方+5ab+3b平方/6ab
=7ab/4ab+(3*4ab+5ab)/6ab
=7/4+17ab/6ab
=7/4+17/6
=21/12+34/12
=55/12