08JUL21

If you want to count a number of vertical bars pointing each of them with your index finger, your hand movement will be horizontal. That is, the X-coordinate is a count of the verticals.


If you want to count a number of horizontal bars pointing each of them with your index finger, your hand movement will be vertical. That is, the Y-coordinate is a count of the horizontals.


All along the X-Axis, the Y-coordinate is zero. Therefore, the equation of the X-Axis is y=0.


All along the Y-Axis, the X-coordinate is zero, Therefore, the equation of the Y-Axis is x=0.


We cannot write an equation for the Origin because it is a point and not a line. Equations exist only for lines and not for points.


A horizontal line 1 unit above the X-Axis has the equation y=1 and a horizontal line 1 unit below the X-Axis has the equation y=-1. Any horizontal line in the Cartesian Plane has the equation y=k.


A vertical line 1 unit to the right of the Y-Axis has the equation x=1 and a vertical line 1 unit to the left of the Y-Axis has the equation x=-1. Any vertical line in the Cartesian Plane has the equation x=k.


If both x and y appear in the equation of a line, it means the line is neither horizontal nor vertical. It's slanting.


Points on the same straight line are said to be collinear. Points not on the same straight line are said to be non-collinear.


A linear equation in x and y represents a straight line.


In math convention, the letters x and y are used to represent variable quantities and letters like a, b, c, m, n, k are used to represent constants (fixed quantities).


For three given points, we can write an equation only if they are collinear.

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