电子课本网 第17页

第17页

信息发布者:
B
D
$x=\sqrt{5}-\sqrt{2}$
$-2$
(1) 证明:$\because\Delta =[-(2m - 1)]^2 - 4×1×(-3m^2 + m)=4m^2 - 4m + 1 + 12m^2 - 4m = 16m^2 - 8m + 1=(4m - 1)^2\geq0,$
$\therefore$无论$m$为何值,方程总有实数根。
(2) 解:由题意知,$x_1 + x_2 = 2m - 1,$$x_1x_2 = - 3m^2 + m。$
$\because\frac{x_2}{x_1}+\frac{x_1}{x_2}=\frac{x_1^2 + x_2^2}{x_1x_2}=\frac{(x_1 + x_2)^2}{x_1x_2}-2=-\frac{5}{2},$
$\therefore\frac{(2m - 1)^2}{-3m^2 + m}-2=-\frac{5}{2}。$
方程两边同时乘以$2(-3m^2 + m)$去分母得:
$2(2m - 1)^2-4(-3m^2 + m)=-5(-3m^2 + m),$
$2(4m^2 - 4m + 1)+12m^2 - 4m = 15m^2 - 5m,$
$8m^2 - 8m + 2 + 12m^2 - 4m = 15m^2 - 5m,$
$20m^2 - 12m + 2 = 15m^2 - 5m,$
移项合并得$5m^2 - 7m + 2 = 0,$
因式分解得$(5m - 2)(m - 1)=0,$
解得$m = 1$或$m=\frac{2}{5}。$
$x^2 - 3x + 2 = 0$
$x^2 + x = 0$
$x^2 + 2\sqrt{2}x + 2 = 0$
$x^2 - 5x + 3 = 0$
$x^2 - 2025 = 0$
解:设这两个数为$x_1,$$x_2$($x_1\leq x_2$)。由题意,可知$x_1,$$x_2$是方程$x^2 - 5x + 6 = 0$的两个根,
对于方程$x^2 - 5x + 6 = 0,$因式分解得$(x - 2)(x - 3)=0,$
则$x - 2 = 0$或$x - 3 = 0,$
解得$x_1 = 2,$$x_2 = 3。$
$\therefore$这两个数分别是$2,$$3。$