Year 7 – Area of Triangles

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To calculate the area of a triangle use the formula:

Area = One half multiplied by the base multiplied by the height  (A=1/2 x bh)



How many triangles?


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Learning Intention: Students will understand how to calculate the area of a triangle, using the rule Area = 1/2 x base x height.

Success Criteria: Students will draw and label at least four different triangles of the same area.

How many different triangles can you draw with an area of 120 cm sq? Use graph paper, where 1 cm ~ 10 cm and label the base and the height, showing any right angles.

Area of a triangle



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Learning Intention: To understand how to calculate the area of a triangle and why the formula (A = 1/2 x base x height) works for all triangles.

Success Criteria: Students will complete the interactive “Area of Triangles” activity with at least 80% of answers correct.

Learning Intentions for this unit

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1. Classify triangles according to their side and angle properties and describe quadrilaterals.

2. Establish the formulas for areas of triangles, rectangles and parallelograms and use these in problem solving.

3. Demonstrate that the angle sum of a triangle is 180 degrees and use this to find the angle sum of a quadrilateral.

Tripods, tricycles and triceratops!

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Learning Intention: To learn to work independently and improve student understanding of angles and triangles, specifically how they are classified.

Success criteria: You will complete all of the activities listed below before next Wednesday.

Sorry I am not at school today – you probably heard my voice failing due to a sore throat this week! While most of our class are at the MWC Winter Sports today (good luck footballers and netballers!) you have a few choices:

1. Page 236 from “Oxford Big Ideas 7” – Classifying triangles.

2. Mathsmate (Term 3, week 3) due tomorrow

3. Mathletics – I have set three new activities for each student about angles and triangles.

4. Go to the National Library of Virtual Manipulatives and choose “Congruent Triangles”. You need to use the sides and angles to create two triangles that look the same.

Measuring Angles, triangles by side length and angle size.


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Learning Intention: You will understand that angles are measured in degrees and be able to name and identify different types of angles and triangles. You will be able to use a protractor effectively and be able to estimate angle sizes.

Success Criteria: You will be able to estimate, draw, measure and identify angles measured in degrees. You will be able to identify, name and draw triangles by side length and by angle size.

This term we will start by measuring angles, using a “rotogram” and then a protractor. You will all need your geometry kit this semester – compass, sharp grey lead pencil, protractor and a good ruler.

What are acute, right, obtuse, straight and reflex angles?
What are equilateral, isosceles and scalene triangles?
What are acute, right and obtuse triangles?
Can you have an equilateral right angled triangle or an obtuse equilateral triangle?
Can you have an obtuse isosceles triangle or a right-angled isosceles triangle?

Task 1: Work in a group of three. Each person should draw and cut out six copies of an equilateral, isosceles or scalene triangle, using different coloured paper. Share your shapes so that each person in the group has two of each type of triangle. Now, tear off the corners of one of each type of triangle and match up the corners to demonstrate the sum of the angles in a triangle.

Task 2: Do the same for acute, obtuse and right angled triangles. Do you think the sum of the angles in a triangle will always be the same? Can you explain why? Do you think the same would be true for quadrilaterals, pentagons and hexagons etc?

The Maths Masters have written a very interesting article in The Age about the triangles in Federation Square.
Read more

Exterior Angles in a Triangle

exterior angles of a triangle

Learning Intention: To understand why, in any triangle, the exterior angle is equal to the sum of the two interior angles not adjacent to it.

Success Criteria: To be able to calculate the missing angles in a triangle, given enough information.



Angles in Polygons


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Learning Intention: Students will understand the relationships between lines, shapes and their angles in triangles, quadrilaterals and other polygons.

Success Criteria: You will be able to calculate the missing angles in various two-dimensional shapes and parallel lines by knowing the sum of the angles of that shape and which angles are equal, complementary or supplementary.

You know that the sum of the angles in a triangle is 180 degrees and in a quadrilateral is 360 degrees, but do you know how to work out the sum of the angles in any polygon? What is an exterior angle? What are complementary and supplementary angles? What are opposite, corresponding, alternate and co-interior angles? These are the questions we will answer in the next unit of work.