JSS1 Third Term Mathematics Lesson Note – Plane Shapes II

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Week 2

TOPIC: PLANE SHAPES

CONTENTS:

• Perimeter of circles and triangles.
• Perimeter of regular quadrilaterals and polygon
• Perimeter of irregular shapes.

MEASURING PERIMETERS

Perimeter is the outside boundary or edge of a plane shape. For example, the boundary fence of your school compound is its perimeter. We also use the word perimeter to mean the length of the boundary.

For example, if you take 200 paces to walk your school boundary, you could say its perimeter is 200 paces.

CIRCLE                         

The Perimeter of a circle is called its CIRCUMFERENCE = 2∏r Where r = radius of a circle and

∏ = 22/7 or 3.14.

EXAMPLE:

The circumference of a Circle is 44cm. Find its diameter.

SOLUTION

Circumference = 2πr

2∏r = 44cm

2 x 22/7 x r   = 44

44/7 x r = 44

Divide through by 44/7

r = 44 ÷ 44/7

r = 44 x 7/44

r =7cm

The diameter of a circle = 2 x

radius, r.

= 2 x 7cm

= 14cm.

2. The circumference of a Circle is 44cm. Find its diameter.

SOLUTION

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