Adjacent angles

<ACD and <BCD are adjacent angles. Move the slider to change the position of the point D.

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1. What are the conditions for a pair of angles to be adjacent?
2. What do you observe as the position of the point D changes?
3. What is the geometric term used to describe a pair of angles whose sum is 180°?
4. Describe fully, the relationship between <ACD and <BCD.

State of New South Wales, Dept. of Education and Training 2007, Created with GeoGebra