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Cartesian system:
• It is a co-ordinate number system used to describe the position of a point by means of two perpendicular lines (horizontal and vertical lines).
• The line $$X'OX$$ is the horizontal line called as the $$x$$ - axis.
• The line $$Y'OY$$ is the vertical line called as the $$y$$ - axis.
Coordinate axes:
The plural form of axis is called the axes. Joining both the lines (horizontal and vertical lines) together at origin is called as the cartesian plane or the coordinate plane.

Signs in the graphs:
• In $$x$$ - axis, the point is positive along the direction $$OX$$ and negative along the direction $$OX'$$.
• In $$y$$ - axis, the point is positive along the direction $$OY$$ and negative along the direction $$OY'$$.