Trig Identity (3) - Geometric Investigation

Drag the point on the semicircle anywhere you can. Then slide the slider slowly.
What is the area of the shaded rectangle on the left in terms of θ?
What is the area of the shaded rectangle on bottom right in terms of θ?
Write an equation that describes the relationship among these 3 areas from the animation you saw above.
– Tim Brzezinski

Information: Trig Identity (3) - Geometric Investigation