This unit was all about concepts related to plane geometry. Plane Geometry mainly deals about flat shapes like lines, angles, triangles, quadrilaterals and other polygons that can be drawn on a piece of paper.

An angle is defined as a surface created by the union of two rays having a common end point. Depending on their size, angles are classified as acute, right, obtuse, straight, reflex and full rotation angles.

When two parallel lines are cut by a third transversal line, the alternate interior angles formed are equal and the corresponding angles are also equal.

A triangle is the simplest polygon with three sides and three interior angles.

Depending on the lengths of their sides, triangles are classified as equilateral, isosceles and scalene.

Based on the size of their angles triangles are also classified as acute, right and obtuse.

Other groups of polygons discussed in this unit are quadrilaterals.

Any four sided geometric figure is called a quadrilateral.

The well-known quadrilaterals are Trapezium, Parallelogram Rectangle, Rhombus, Square and Kite. Each has its own specific meaning and property.

• Trapezium/Trapezoid: is a quadrilateral which has only one pair of opposite sides parallel
• Parallelogram: is a quadrilateral which has two pair of opposite sides parallel
• Rectangle: is a parallelogram with four right angles
• Rhombus: is a parallelogram with four equal sides
• Square: is a parallelogram with four equal sides and four right angles
• Kite is a quadrilateral with two pairs of adjacent sides equal