1.
根号下5减2倍根号6
=根号(（根号3-根号2）^2)
=根号3-根号2
2.
√xy / (y√x-x√y)
=√xy / (√xy^2-√x^2y)
= √xy /(√xy (√y-√x))
=1 / (√y-√x)
=(√y + √x) / (y - x)^2是 什么意思 ...平方 x^2 = x*x