Unfortunately, IKeudin's project is misleading. Tangent is not used for finding lengths in the way he showed. That was Pythagorean Theorm.
Tangent can be used for finding lengths of a right triangle from this though:
Tan (angle) = opposite / adjacent
I've seen some people make art/designs with tangent, but mostly in Hopscotch you're going to use inverse tangent (or arctan) to find the angle between 2 objects (i.e., point towards)
angle = arctan( opposite / adjacent)
Here's a couple examples of how to use it: