(a+2b)/(a-2b)=2
原式=1/2*[(a+2b)/(a-2b)]+(3/4)*[(a+2b)/(a-2b)]
=1/2*2+3/4*2
=5/2求代数式2（a-2b）分之a+2b加上4a-8b分之3a+6b的值做了没看懂，讲讲(3a+6b)/(4a-8b)=[3(a+2b)]/[4(a-2b)]=(3/4)*[(a+2b)/(a-2b)]