Myths about teaching can hold you back
- Year 9
Choosing an appropriate method for finding lengths of a triangle
I can choose the appropriate method to find the missing side in a right-angled triangle.
- Year 9
Choosing an appropriate method for finding lengths of a triangle
I can choose the appropriate method to find the missing side in a right-angled triangle.
Lesson details
Key learning points
- Trigonometry can be useful in many practical situations.
- You can use it to find the height of objects.
- You can use it to find the length of an object given the length of its shadow.
- Sometimes it may be better to use Pythagoras' theorem.
Keywords
Trigonometric ratios - The trigonometric ratios are ratios between each pair of lengths in a right-angled triangle.
Common misconception
Pupils may struggle to find a right-angled triangle within the context of the question.
Encourage the pupils to sketch the question and consider adding a perpendicular line to the diagram.
To help you plan your year 9 maths lesson on: Choosing an appropriate method for finding lengths of a triangle, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Choosing an appropriate method for finding lengths of a triangle, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 maths lessons from the Trigonometry unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.In a right triangle, if the hypotenuse is 40 cm and a second side is 32 cm, what is the length of the third side? (Use a calculator to help you.)
Q2.In a right triangle, if the shortest sides are 10 cm and 7.5 cm, what is the length of the hypotenuse? (Use a calculator to help you.)
Q3.Would a triangle ABC with sides AB = 9cm, BC = 7.5cm, AC = 12.5cm be similar to the one shown in the diagram?

Q4.For this pair of triangles, can you determine whether they are similar without using side lengths?

Q5.In a right triangle, if the hypotenuse is 200 cm and a second side is 120 cm, what is the perimeter? (Use a calculator to help you.)
Q6.In a right triangle, if the hypotenuse is 30 cm and a second side is 18 cm, what is the area? (Use a calculator to help you.)
Assessment exit quiz
6 Questions
Q1.This robot standing on a box has a fly on the top of their head. How high up (h) is the fly from the ground?

Q2.This robot standing on a box has an ant on the top of their head. How high up (h) is the ant from the ground to 2 d.p. ?

Q3.If the area of square ABCD is $$25 cm^2$$, what is the length of the diagonal BD to 2 d.p. ?
