求问陈向东P257第17题

olynn

In the xy-plane, line k is a line that does not pass through the origin. Which of the following statements individually provide sufficient additional information to determine wheter the slope of line k is negative?
其中A是The x-intercept of line k is twice the y-intercept of line k

可是截距不是绝对值吗？这怎么能判断呢？...

dennyanddemi

我貌似记得OG上说了截距就是有正负的，应该是一句很短的话，楼主翻翻前面的知识点？
这个题目是不是这样 Y=kx+b,  分别把x=0, y=0 带入，得到x=-b/k, y=b, x=2b, 算出k=-1/2。
我数学不好，错了别怪我。。。

gaoxsn

截距是坐标值不是绝对值。
横纵截距同号，斜率必为负。