a-2b/a+2b=3
a-2b=3（a+2b)
a-2b=3a+6b
-2a=8b
a=-4b
所以,
2+(2b/a)-2b+3a-(6b/4a)+8b
=2+（2b/-4b）-2b+3（-4b)-（6b/-16b）+8b
=2-(1/2)-14b+(3/8)+8b
=3/2+3/8-6b