# Circle facts and theorems

Topic:
Circle

## Circle Theorem 1

Move points A, B and C on the circumference. The pink lines are radii. What do you notice about the angles? Conjecture (idea for what the rule might be): Justification (using rules you already know):

## Circle Theorem 2

Move points A, B and C on the circumference and look at how the angles change. Is it possible to make one of the angles = 90 degrees? Conjecture (idea for what the rule might be): Justification (using rules you already know):

## Circle Theorem 3

Move any of the points on the circumference. What do you notice about the 2 angles shown? Conjecture (idea for what the rule might be): Justification (using rules you already know):

## Circle Theorem 4

Move any of the points on the circumference. What do you notice about the angles? (hint: look at angles opposite each other) Conjecture (idea for what the rule might be): Justification (using rules you already know):

## Circle Theorem 5

Move any of the points on the circumference. The blue line is a tangent to the circle. What do you notice about the angles? Conjecture (idea for what the rule might be): Justification (using rules you already know):

As an extension can you represent your rules in algebraic form? (write them down on paper)