In any given coordinates (x,y), the sign of abscissa i.e, x coordinate and the sign of ordinate i.e. y coordinate, both together decide the quadrant in which the pont lies.
If both x and y are positive, the point lies in first quadrant;
if x coordinate is negative and y coordinate is positive, the point lies in second quadrant;
if both x and y are negative, the point lies in third quadrant; and
if x coordinate is positive and y coordinate is negative, the point lies in fourth quadrant.
Graphically it can be shown as in image below.
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In (-1,-2) as both x and y are negative, the point lies in third quadrant.
