Chapter 1 - Section 1.2 - The Rectangular Coordinate System - 1.2 Problem Set - Page 23: 20

Quadrant 4

to create a negative ratio of $x/y$ one must remember that the only way for the ratio to be negative would be if one value is positive and the other value is negative, now, we know this is true in in Quadrant 2, but it is also true for quadrant 4 as the the $x$ value is positive and the $y$ value is negative