# 3D Trigonometry: Get 21 – TES Resource of the Week 68

What is it?

There are two areas of mathematics that my lovely Year 11 class are a little bit dodgy at. One is 3D Trigonometry – and I can sympathise here as my lack of any kind of spatial awareness makes these extra dimension problems more than a little tricky. And the other is knowing that there answer is sensible. Countless times we have had 4.5kg for the weight of a car, or even (and I am wincing typing this) a probability greater than 1! So, imagine my delight when I came across this resource that can help alleviate both these deadly ailments. There are some really nicely selected questions on 3D trigonometry, calling upon students’ knowledge of Pythagoras and SOHCAHTOA, but then there is a nice little twist…

How can it be used?

As the instructions clearly explain, students are to answer one of the questions in a given time limit (the author suggests 4 minutes), and then they have one minute to select the next question they are working on. The aim is that the answers to both questions should be as close to 21 as possible, so the choice of the second question is crucial. During that minute students should be rounding, estimating and doing mental calculations to try to get a feel of the approximate answers to each question. They can then complete the question and see how far off they were. So, students get plenty of practise of a key topic and have an opportunity to hone their estimation skills, all with a little bit of competition thrown in for good measure!

Thank you for sharing!

Craig Barton