(1)因x,y＞0.故x+y≥2√(xy).===>2(x+y)≥(√x+√y)².===>√[2(x+y)]≥√x+√y.===>(√x+√y)/√(x+y)≤√2.（2）题中不等式可化为a≥(√x+√y)/√(x+y).故由上可知,a≥√2.