Pythagoras' Theorem and pizzas? The theorem is meticulously described here with an animation and extension material that brings the concept to real life (yes, using pizzas!). Among various other sections covered are sine, cosine, tangent and measurements in radians.
A common mathematical problem is to find the angles or lengths of the sides of a triangle when some, but not all, of these quantities are known. It is also useful to be able to calculate the area of a triangle from some of this information. Video tutorial 40 mins.