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What Does Bisecting an Angle Mean?

In this section, you’ll learn to bisect and copy angles. I’ve made two set of instructions—one for bisecting, and one for copying—to make it as easy for you as possible.

Bisecting an Angle

Angle with angle bisector

Rule

Instructions for Bisecting an Angle

1.: Put the point of the draft compass on the vertex $V$ .
2.: Make an arc that intersects both sides of the angle. Call the intersections $A$ and $B$ .
3.: Next, put the point of the draft compass on $A$ and make a small arc approximately in the middle of the angle.
4.: Move the point of the draft compass to $B$ without changing the distance between the legs of the draft compass, then make a small arc that intersects with the arc you drew in the previous step.
5.: Draw a line from the vertex through the point where the two small arcs intersect.
6.: The line you just drew splits the original angle into two equal angles.

Copying an Angle

Copy of an angle

Rule

Instructions for Copying an Angle

1.: Draw a line $l$ and mark a point $P$ on it.
2.: Put the point of the draft compass on the vertex $V$ of the original angle (the angle you want to copy).
3.: Make an arc that intersects both sides of the original angle. Call the intersection between the arc and the left side of the angle $A$ , and call the intersection between the arc and the right side of the angle $B$ .
4.: Without changing the distance between the legs of the draft compass, put the point on $P$ and make the same kind of arc as in the previous step. Call the intersection between the line $l$ and the arc, $B^{'}$ (“B prime”).
5.: Set the distance between the legs of the draft compass to the distance between $A$ and $B$ .
6.: Without changing the distance between the legs of the draft compass, put the point on $B^{'}$ and make a small arc that intersects the arc you made in Step 4. Call the intersection $A^{'}$ (“A prime”).
7.: Draw a line from $P$ through $A^{'}$ . You have now copied an angle.

Constructing a 90°, 45° or 22.5° Angle

How Do You Rotate a Figure?

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