11.1 RECTANGULAR COORDiNATE AXES
To locate a point in a plane, two numbers are necessary. We know that any point in the xy plane can be represented as an ordered pair (a, b) of real numbers where a is called x-coordinate of the point and b is called the y-coordinate of the point. For this reason, a plane is called two dimensional.
To locate a point in space, three numbers are required. Any point in space is represented by an ordered triple (a, b, c) of real numbers. To represent a point in space we first choose a fixed point ‘O’ (called the origin) and then three directed lines through O which are perpendicular to each other (called coordinate axes) and labelled x-axis, y-axis as being horizontal and z-axis as vertical ...