b=√(3-5a）+√(5a-3)+15
√(3-5a)>=0
a=0
a>=3/5
所以a=3/5,b=15
b>a
√（b/a+a/b+2）-√(b/a+a/b-2)
=√[(a^2+b^2+2ab)/ab]-√[(a^2+b^2-2ab)/ab]
=√[(a+b)^2/ab]-√[(a-b)^2/ab]
=(a+b)/√(ab)-(b-a)/√(ab)
=2a/√(ab)
=(2*3/5)/√(15*3/5)
=(6/5)/√9
=6/5*1/3
=2/5