What is a circle?
A circle is the trace of one point moving at a constant distance from another point which we call the center.
As the green point moves round the center (red dot)keeping the same distance away, it traces a circle (blue).
The distance from any point on the circle to the center is called the radius (black line).
A straight line from any point on the circle through the center to the other edge of the circle is called the diameter of the circle. It divides the circle in two. The purple line is the diameter.
The distance from any point on the circle to the center is called the radius (black line).
A straight line from any point on the circle through the center to the other edge of the circle is called the diameter of the circle. It divides the circle in two. The purple line is the diameter.
A continuous part of a circle is called an arc. The blue part is an arc of the red circle.
A straight line that touches a circle at one point is called a tangent.The yellow line is a tangent.
A straight line that touches a circle at one point is called a tangent.The yellow line is a tangent.
Geometry: using only compasses and straightedge