狗狗26还是不能确定吗

森然

A vertical line's slope is undefined meaning it has "no slope."---wiki

Verdict: vertical lines have NO SLOPE. In particular, the concept of slope simply does not work for vertical lines.
----http://www.purplemath.com/modules/slope.htm

网上找的关于slope的数学概念
如果最后推出n＝0，即y轴，slope是不存在的。所以问 is slope>0?回答是no，所以是C

讨论下吧，很confusing，关键是slope到底是理解成不存在，还是可以等于负无穷到正无穷呢？

-- by 会员 naturalwater (2010/8/14 22:14:16)

我们来想想tant的图吧，是不是两条那样的，一个趋近于正无穷，一个趋近于负无穷~所以我坚定的认为应该选E

-- by 会员 魏小妞要出国 (2010/8/14 22:17:15)

for  C~
以下蓝红色字摘自prep模考上的math review：

For any two points on the line, the slope is defined to be the ratio of the difference in the y-coordinates to the difference in the x-coordinates.
——个人认为：用tan表示斜率是计算上的需要，并不是斜率的定义：y方向上变量与x方向上变量之比。垂直于X轴的直线，y方向上变量无论多少，x方向上变量恒为0，即y方向上变量与x方向上变量无相关性。所以不存在“the ratio，之比”，即不存在“斜率”。
Negative vs. positive slope of a lineIf the slope of a line is negative, the line slants downward from left to right; if the slope is positive, the line slants upward. If the slope is 0, the line is horizontal; the equation of such a line is of the form y = b
since m = 0. For a vertical line, slope is not defined, and the equation is of the form x = a, where a is the x-intercept.
1+2推出来是：该线重合y轴，是vertical line, 所以它斜率not defined，即可判断原命题为：NO
综上：选C