Creation of this resource was inspired by this [url=https://twitter.com/solvemymaths/status/1103364683808075777]problem[/url] posed by [url=https://twitter.com/solvemymaths]Ed Southall[/url]. [br][br]You can move the vertices of the triangle anywhere you'd like at any time. [br]The [b][color=#0000ff]blue slider[/color][/b] controls the size of the [b][color=#0000ff]angle with blue vertex[/color][/b]. [br][br][b][color=#ff00ff]How can we formally prove what is dynamically illustrated here?[/color][/b]