Trig Identity via Areas: Dynamic Illustrator

[size=150]Feel free to move the [b][color=#ff00ff]LARGE POINT[/color][/b] anywhere you'd like on either graph. [br][/size][br][size=150][b][color=#1e84cc]What trigonometric identity is dynamically being illustrated here? [/color][/b][/size]
Slowly slide the vertical slider (you see on the right) upwards.

Information: Trig Identity via Areas: Dynamic Illustrator