Exterior region the portion of the plane outside the curve is called the exterior region.

Interior region the portion of the plane inside the curve or bounded by the curve is called the interior region.

Exterior of an angle

The cavity in the region of diencephalon in the brain is called the

The region of water on the surface of the earth is called the

Exterior the part of the plane which is outside the arms of an angle produced indefinitely is called the exterior of the angle.

Exterior the part of the plane consisting of those points P for which OP>r is called the exterior of the circle with centre O and radius r.

THEOREM (Exterior Angle Property of a Triangle): If a side of a triangle is produced the exterior angle so formed is equal to the sum of two interior opposite angles.

Exterior angle theorem: If a side of a triangle is produced; the exterior angle so formed is equal to the sum of the two interior opposite angles.