【x²-1分之3x-3】÷【x+1分之3x】-【x-1分之1】
=[3(x-1)/(x+1)(x-1)]÷[3x/(x+1)]-[1/(x-1)]
=[3(x-1)/(x+1)(x-1)]*[(x+1)/3x]-[1/(x-1)]
=(1/x)-[1/(x-1)]
=(1/2)-[1/(2-1)]
=(1/2)-1
=-0.5