Question

先化简再求值

Answer 1

=-(a+b)(a-b)/a(a-b) ÷(a²+2ab+b²)/a×(b+a)/ab
=-(a+b)(a-b)/a(a-b) ×a/(a+b)² ×(a+b)/ab
=-1/ab
当a=√2+√3 b=√2-√3时
原式=-1/(√2+√3)(√2-√3)
=1

Answer 2

原式=-(a+b)(a-b)/a(a-b)÷(a²+2ab+b²)/a×(a+b)/ab
=-(a+b)/a×a/(a+b)²×(a+b)/ab
=-1/(a+b)×(a+b)/ab
=-1/ab
=-1/(2+√3)(2-√3)
=-1/(4-3)
=-1