Circles and Construction Tools: Practice

Among points in that plane, circle membership means that the distance from $O$ is exactly $r$. The required condition is $OP=r$.

A disk contains the boundary and interior. The word circle denotes the boundary alone.

The circle's defining condition is that every point on it is $8$ cm from $O$. Since $A$ is on the circle, $OA=8$ cm.

A diameter consists of two radii end to end.

$2\times6=12$

Its length is $12$ cm.

The endpoint condition defines a chord: both endpoints must lie on the circle. Passing through the center is an extra condition for a diameter.

A diameter is a chord passing through the center. Its orientation on the page does not matter.

The compass point stays at the center while the pencil stays one opening away. That opening is the radius.

An unmarked straightedge joins distinct points or extends their line. It has no scale for reading lengths or angles.

The radius of the circle centered at $P$ is $AB$. Its point $Q$ therefore satisfies $PQ=AB$.

The first circle is centered at endpoint $A$ with opening $AB$. It makes every point on that circle a distance $AB$ from $A$.

Circle $A$ gives $AC=AB$, and circle $B$ gives $BC=AB$. Thus all three triangle sides have the same length.

Copy the distance between the two source marks, chord $AB$. This setting locates the second target mark on the target circle.