√b/(√a-√b)-√b/(√a+√b)
={√b(√a+√b)-√b(√a-√b)}/(√a-√b)(√a+√b)
=(√ab+b-√ab+b)/(a-b)
=2b/(a-b)
=2x1/4/(1/2-1/4)
=1/2÷ 1/2
＝1