The first quadrant of graph is taken as positive because in the horizontal line, x axis, (0,0) the right side of the line from 0 is considered to be positive and the left side is considered to be negative. In the vertical line, y axis, (0,0) the upper side of the line is considered to be positive and the lower side of the line is negative. Thus, the 1st quadrant is positive. As we must first consider the x-axis and then the y-axis. The 1st quadrant is positive, the 2nd quadrant is negative positive, the 3rd quadrant is negative and the fourth quadrant is positive negative.
Hope that might help you........^_^