An underpinning is “a solid foundation laid below ground level to support or strengthen a building”. Here, we are building a knowledge base for trigonometry. This 12 minute video explores some important special relationships.

There are no specific practice questions attached to this video. But, you should now be ready for the following video:

https://mathpqjq.com/trigonometry-finding-sides-and-angles/

and the practice questions that follow.