The equation of a circle
A dynamic animation which can be used to promote the understanding of the equation of a circle.
Questions to ask, focusing specifically on variation and change
(students should be given iPads for this task):
Can you change one aspect of the equation to make the circle have a larger area?
Can you change one aspect of the equation so it is contained entirely in one quadrant?
Can you change one aspect of the equation so that it touches the y axis?
Can a circle touch the x, and the y axis, at the same time? What parameter values do you have if so?
Can the circle be in only two quadrants?
Is it possible for the circle to be contained in three quadrants?