One full turn of the hand is 1 revolution.

A right angle is ¼ revolution and a straight angle is ½ a revolution. We use a protractor to measure the size of an angle in degrees.

The measure of a right angle is 90° and hence that of a straight angle is 180°.

An angle is acute if its measure is smaller than that of a right angle and is obtuseif its measure is greaterthan that of a right angle and less than a straightangle.

A reflex angle is largerthan a straight angle.

Two intersecting lines are perpendicular if the anglebetween them is 90°.

The perpendicular bisector of a line segmentis a perpendicular to the line segmentthat divides it into two equal parts.

Triangles can be classified as follows based on their angles:

Triangles can be classified as follows based on the lengths of their sides:

Polygons are namedbased on theirsides.

Quadrilaterals are furtherclassified with reference to their properties.

·We see aroundus many three dimensional shapes.Cubes, cuboids, spheres,

cylinders, cones,prisms and pyramidsare some of them.