The problem says " Two forces of magnitudes 12 and 15 newton are applied to a point and the tangesnt of the angle between them is -3/4. Find the resultant of the two forces and the measure of its angle of inclination on the first force. In the answer it says that the theta belongs to the second quad, and I assume this is because the tan -ve but why didn't it assume it's in the fourth quad? And why doess the -ve sign belong to the 4 on the x-axis not the 3 on the y-axis??