(x-1分之1-x+1分之1)/2x的平方-2分之x
=[(x+1-x+1)/(x-1)(x+1)]/2x²-x/2
=1/x²(x-1)(x+1)-x/2 x=2
=1/[2²*(2-1)(2+1)]-2/2
=1/12-1
=-11/12