第10页 - 通城学典课时作业本九年级数学人教版南通专版

D

A

-1

$k\geq -\frac{1}{3}$

 解：$\because\Delta = 3^2 - 4\times2\times(-4)=9 + 32 = 41＞0，$$\therefore$方程有两个不等的实数根

 解：$\because\Delta = (-6\sqrt{2})^2 - 4\times1\times18 = 72 - 72 = 0，$$\therefore$方程有两个相等的实数根

 解：原方程化为一般式为$5x^2 - 7x + 5 = 0，$$\because\Delta = (-7)^2 - 4\times5\times5 = 49 - 100 = -51＜0，$$\therefore$方程无实数根

 解：$\because$关于$x$的方程$x^2 - 2x + 2m - 1 = 0$有实数根，$\therefore\Delta = 4 - 4(2m - 1)\geq0，$即$4 - 8m + 4\geq0，$$8 - 8m\geq0，$$8m\leq8，$解得$m\leq1。$$\because m$为正整数，$\therefore m = 1。$$\therefore$原方程可化为$x^2 - 2x + 1 = 0，$即$(x - 1)^2 = 0，$解得$x_1 = x_2 = 1$

D