分子分母同时乘以（根号2+1）分母等于1分子等于（根号2+1）结果就是（根号2+1）
化简不了吧，要不就等于无理数0.41421356...要不就等于√2-1
=(√2+1)/[(√2-1)(√2+1)]=(√2+1)/(2-1)=√2+1
1/√2-1=(√2+1) / (√2+1)(√2-1)=(√2+1) / [ (√2 )^2+√2-√2-1]=1+√2
