|x-1/2x-3|+（3y+1/y+4）^2=0
两个非负数之和为0,那么这两个数都是0
(x-1)/(2x-3)=0
x=1
(3y+1)/(y+4)=0
y=-1/3
3/(2x+1)-2/(3y-1)
=3/(2*1+1)-2/[(-1/3)*3-1]
=1+1
=2