Three points A, B and C lie in this order on a line, and P is any
point in the plane. Use the Cosine Rule to prove the following
Three squares are drawn on the sides of a triangle ABC. Their areas
are respectively 18 000, 20 000 and 26 000 square centimetres. If
the outer vertices of the squares are joined, three more triangular
areas are enclosed. What is the area of this convex hexagon?
An observer is on top of a lighthouse. How far from the foot of the lighthouse is the horizon that the observer can see?
Look at the film below - does that fit with your description?
Look especially at Stage 3 of the film, you may also find the Pause button useful.