These videos are examples of the ‘finding the missing angle' types of questions. They can be a little challenging, although I hope that the examples will give you an overview of the range of GCSE maths problems.
Unfortunately there isn't really a specific topic; these problems are more about solving. You might need circle theorems, and also properties of regular polygons – particularly that the external angles add to 360 degrees. For the second question, you need also need to know that two of a regular polygons sides, can be used to form an isosceles triangle.
Here are the questions: Finding the missing angle.
…. and here are the answers: Finding the missing angle ANSWERS
The problems are aimed at around grade 6, and the topic appears in all the main examination boards, including Edexcel, AQA and OCR. Finding ‘x' in a shape is reasonably popular, as you need to be familiar with a few geometry and algebra concepts.
Please do stop the video, try the questions and compare your solution.
I hope the videos help and please leave a comment below, if you are not sure. Alternately you can view my YouTube channel and leave a comment there – I'll always try to respond as quickly as possible.
Watch the videos on YouTube:
Here's a few additional (although older) posts on finding x's:
It might also be worth viewing: