先化简,后求值 ,x的2次方减2x分之x的2次方减1除(x-1-2x-1分之x+1).其中x=2分之1

(x^2-1)/(x^2-2x)÷[x-1-(x+1)/(2x-1)]
=(x+1)(x-1)/x(x-2)÷[(x-1)(2x-1)/(2x-1)-(x+1)/(2x-1)]
=(x+1)(x-1)/x(x-2)÷{[(x-1)(2x-1)-(x+1)]/(2x-1)}
=(x+1)(x-1)/x(x-2)÷[(x^2-4x)/(2x-1)]
=(x+1)(x-1)(2x-1)/x^2(x+2)(x-4)
x=1/2
=3/2*-1/2*-1/(1/4*5/2*-7/2)
=-3/4*8/23
=-6/23