Mathematics - Junior Secondary 2 - Angles and polygon

Angles and polygon

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TERM: 3RD TERM

WEEK 2

Class: Junior Secondary School 2
Age: 13 years
Duration: 40 minutes of 5 periods
Subject: Mathematics
Topic: Angles and Polygon
Focus: Generalization of Interior Angles of Polygons

SPECIFIC OBJECTIVES:

By the end of the lesson, pupils should be able to:

  1. State and apply the formula for calculating the sum of interior angles of polygons: (2n – 4) right angles for a convex polygon.
  2. Solve problems on the interior angles of convex polygons.

INSTRUCTIONAL TECHNIQUES:

  • Question and answer
  • Guided demonstration
  • Problem-solving
  • Interactive activities
  • Visual aids

INSTRUCTIONAL MATERIALS:

  • Whiteboard and marker
  • Protractors
  • Worksheets

 

PERIOD 1 & 2: Generalizing the Sum of Interior Angles of Polygons

PRESENTATION:

Step

Teacher’s Activity

Pupil’s Activity

Step 1 - Introduction

Explains the formula for calculating the sum of the interior angles of a polygon.

Pupils listen and take notes.

Step 2 - Explanation

Demonstrates how to apply the formula (2n – 4) right angles for a convex polygon.

Pupils ask questions and follow the explanation.

Step 3 - Demonstration

Solves example problems with the class using the formula.

Pupils follow and solve similar problems with guidance.

Step 4 - Practice

Pupils solve problems involving calculating the sum of interior angles for different polygons.

Pupils work individually or in groups to solve problems.

NOTE ON BOARD:

  • Formula for sum of interior angles of a convex polygon:
    (2n–4)×90°(2n – 4) \times 90°, where nn is the number of sides of the polygon.

EVALUATION (5 exercises):

  1. Calculate the sum of interior angles of a hexagon.
  2. Find the sum of the interior angles of a quadrilateral.
  3. Solve for the sum of interior angles of an octagon.
  4. Calculate the sum of the interior angles of a pentagon.
  5. Apply the formula to find the sum of the interior angles of a 7-sided polygon.

CLASSWORK (5 tasks):

  1. Calculate the sum of interior angles for a polygon with 5 sides.
  2. Solve for the sum of the interior angles of a hexagon.
  3. Find the sum of interior angles of a 10-sided polygon.
  4. Calculate the sum of interior angles of a triangle.
  5. Solve a problem involving a polygon with 8 sides.

ASSIGNMENT (5 questions):

  1. Find the sum of interior angles of a 12-sided polygon.
  2. Solve a problem where the sum of interior angles of a polygon is given as 1620° and find the number of sides.
  3. Calculate the sum of interior angles for a nonagon.
  4. Solve a problem involving an irregular polygon with 6 sides.

Write a story problem based on polygons and their interior angles.