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When teaching solving 3D problems using trigonometry we begin the lesson with a recap of Pythagoras’ Theorem and the three trigonometric ratios. We do this by matching the ratio and equations to the respective right-angled triangle.

Students are encouraged to work in pairs and to show the diagrams as part of the working out on mini-whiteboards. A nice way to differentiate this is to have the less able student do the writing. I check to see whether they can correctly label the sides as this helps to know whether to use Sine, Cosine or Tangent.

When solving 3D problems involving trigonometry, I demonstrate how to identify the right-angled triangle containing the unknown side or angle and sketch it out separately. If there is not enough information given about this triangle, we look for further clues in another triangle involving the same line or angle. Check out the video below for a quick demonstration.

To check the student’s understanding and progress we work through some examples from the Interactive Excel File on mini-whiteboards.

Students are asked to sketch out the necessary right-angled triangles needed to find the length FB and angle FBG. Without explaining how, I ask them to calculate the length FB and show me their working on mini-whiteboards. It is interesting that a couple of students try to apply the Cosine Rule to triangle FBG. We feedback how to use Pythagoras’ Theorem to address the misconceptions.

Next, I ask students to use this new information to calculate angle FBG. Some struggle to use the correct ratio but all students attempt to solve it as a right-angled triangle using either Sine, Cosine or Tangent.

I use the solving 3D problems using trigonometry Interactive Excel File to pose a different, but similar question for the class to attempt again on mini-whiteboards. All students sketch the two relevant right-angled triangles. Some continue to struggle calculating the angle using the correct trigonometric ratio but all students correctly calculate the length FB using Pythagroas’ Theorem.

The plenary challenges the class to identify the necessary right-angled triangles independently. I provide a handout of the shape to some students so they can annotate the drawing. After a couple of minutes of attempting the problem independently we stop the lesson to discuss different approaches. This provides a starting point for some students while reassuring others. The plenary problem normally takes between 10 to 12 minutes. To end the lesson, I ask a willing student to demonstrate their working at the front of the class to their peers. We address any misconceptions as they arise.

July 6, 2019

Earlier this week, my school took part in a trial OFSTED inspection as part of getting ready for the new inspection framework in September 2019. This involved three Lead Inspectors visiting our school over the course of two days. The first day involved a ‘deep dive’ by each of the Lead Inspectors into Mathematics, English […]

June 30, 2019

The method of how to solve quadratics by factorising is now part of the foundational knowledge students aiming for higher exam grades are expected to have. Here is an example of such a question. Solve x2 + 7x – 18 = 0 In my experience of teaching and marking exam papers students often struggle with […]

June 24, 2019

When learning how to write 3-part ratios students need to understand how ratios can be made equivalent. The start of the lesson reminds students by asking which of six ratios is the odd one out. This is presented to the class as they come into the lesson. Writing Equivalent Ratios A few students immediately go […]