即(4a²-4a+1)+(b²-6b+9)=0
(2a-1)²+(b-3)²=0
所以2a-1=b-3=0
a=1/2,b=3
所以原式=2a√a+√ab-a√a-5√ab
=a√a-4√ab
=√2/4-4√6/2
=√2/4-2√6