因为代数式 a+b/a-b=2,所以a-b/a+b=1/2
则(3a+3b/5a-5b)-(3a-3b/2a+ab)
=3/5×(a+b/a-b)-3/2×(a-b/a+b)
=3/5×2-3/2×1/2
=6/5-3/4
=9/20