In coordinate geometry, points are placed on the "coordinate plane" as shown below. It has two scales - one running across the plane called the "x axis" and another a right angles to it called the y axis. (These can be thought of as similar to the column and row in the paragraph above.) The point where the axes cross is called the origin and is where both x and y are zero.

On the x-axis, values to the right are positive and those to the left are negative. 
On the y-axis, values above the origin are positive and those below are negative.
A point's location on the plane is given by two numbers,the first tells where it is on the x-axis and the second which tells where it is on the y-axis. Together, they define a single, unique position on the plane. So in the diagram above, the point A has an x value of 20 and a y value of 15. These are the coordinates of the point A, sometimes referred to as its "rectangular coordinates". Note that the order is important; the x coordinate is always the first one of the pair.For a more in-depth explanation of the coordinate plane see The Coordinate Plane. 
For more on the coordinates of a point see Coordinates of a Point

Things you can do in Coordinate GeometryIf you know the coordinates of a group of points you can:Determine the distance between themFind the midpoint, slope and equation of a line segmentDetermine if lines are parallel or perpendicularFind the area and perimeter of a polygon defined by the pointsTransform a shape by moving, rotating and reflecting it.Define the equations of curves, circles and ellipses.
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