先化简再求值;2x-6/x^2-4x+4÷4x-12/x^2-4÷(x+2),其中x=1/2

题目

先化简再求值;2x-6/x^2-4x+4÷4x-12/x^2-4÷(x+2),其中x=1/2

答案

2x-6/x^2-4x+4÷4x-12/x^2-4÷(x+2)
=2x-4x-6/x^2-12/x^2+4÷4x-4÷(x+2)
=-2x-1/4x+1/x-1/(x+2)
将x=1/2带入,原式得
=-2*1/2-1/2+2-2/5
=1/2-2/5
=-1/10