Show this first animation and ask, what do you notice? What do you wonder?
Then ask the following: If the diameter of the circle is 8 cm. What (or when) is the largest area? What are the dimensions of this triangle?
After students solve that pose, When is the area exactly half the largest? What are the dimensions of that triangle? What is the angle?
After some work time and playing around with the above problem, show them this animated version