JSS1 Third Term Mathematics Lesson Note – Plane Shapes

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WEEK 1

TOPIC: PLANE SHAPES.

CONTENT

• Identification of plane shapes
• Properties of circles and triangles
• Properties of quadrilaterals: square, rectangle, trapezium, rhombus, parallelogram, and kite
• Identification and naming of polygon
• Similarities and differences between regular quadrilaterals.

Identification of plane shapes

A flat surface, such as top of a table, a playing field, ceiling, wall, face of a tin and star board face is referred to as a plane. It is a plane because it is two dimensional, i.e. it is measured in only two directions.

Figures drawn on flat or plane surfaces are called plane shapes. Examples include rectangle, square, triangle, parallelogram and trapezium.

All these shapes are referred to as a regular shape, i.e. they have definite length and breadth.

There are also irregular shapes (they do not have definite length and breadth), e.g. leaves, stones, etc.

Circle

The shape traced out in which every point of it is same distance from a fixed centre point is called circle.

The outer –boundary of the circle is called the circumference. The curved part of the circumference is called arc. The radius is the straight line joining the centre to any part on the circumference.

The straight line that divides the circle into semicircles is called the diameter. The line that divides the circle into two segments is called the chord.

The region bounded by the diameter and the arcs of a circle is called the semi- circle. The sector is the region bounded by two radii and the arc of the circle. The segment is the region bounded by the chord and the arc of the circle. A circle has infinite number of lines of symmetry

CLASS ACTIVITY

1) How many lines of symmetry have a circle?

2) Describe the following parts of a circle a) radius b) sector c) segment d) chord e) diameter.

Triangles

Definition: A triangle is a closed figure made up of three line segments.

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