# Usual Topology on Real

**Usual Topology on **

A collection of subsets of which can be can be expressed as a union of open intervals forms a topology on , and is called topology on .

**Remark:**

Every open interval is an open set but the converse may not be true.

**Usual Topology on **

Consider the Cartesian plane , then the collection of subsets of which can be expressed as a union of open discs or open rectangles with edges parallel to the coordinate axis from a topology, and is called a usual topology on .

**Usual Topology on **

Consider the Cartesian plane , then the collection of subsets of which can be expressed as a union of open spheres or open cubed with edges parallel to coordinate axis from a topology, and is called a usual topology on .