Parallelogram: Theorem 2

Interact with the applet below for a few minutes. [br]Then, answer the questions that follow. [br][br]Feel free to move the BIG WHITE POINTS anywhere you'd like! [br][color=#ff00ff]You can also adjust the size of the pink angle by using the slider. [/color]
1.
What special type of quadrilateral was formed in the first half of your sliding-the-slider? How do you know this?
2.
What else can you conclude about this special type of parallelogram? Be specific!
3.
In the special quadrilateral above, [color=#ff00ff]suppose the pink angle measures 110 degrees[/color]. [color=#0000ff]What would the measure of the blue angle be?[/color] What would the measure of each interior angle of this special quadrilateral be?
4.
Write a 2-column or paragraph proof of what you've informally observed here. (Hint: This proof will involve a pair of congruent triangles!)
Quick Demo: 0:33 sec to 1:16 sec (BGM: Andy Hunter)
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Information: Parallelogram: Theorem 2