a平方+b平方/a平方-b平方减a+b/a-b除以2ab/（a-b)(a+b)平方
=[(a²+b²)/(a+b)(a-b)-(a+b)²/(a+b)(a-b)]×（a-b）（a+b）²/2ab
=[-2ab/(a+b)(a-b)]×（a-b）（a+b）²/2ab
=-(a+b)
=-(√2-1+3)
=-√2-2