Adjacent angles

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

1. What do you observe when you move the point D?
2. Write down the properties of adjacent angles.
3. What is the geometric term used to describe angles whose sum is 90°?
4. Describe fully, the relationship between <DCF and <BCD.

State of New South Wales, Dept. of Education and Training 2007, 25/9/07, Created with GeoGebra