There are different types of segment bisectors that define bisecting a line. Constructing Perpendicular Bisectors – Explanation and ExamplesĬonstructing a perpendicular bisector with a compass and straightedge requires that we first find the center of a line segment and then construct a line perpendicular to that point.A segment bisector divides a line into two or more equal parts. How to Construct the Perpendicular Bisector of a Triangle.How to Construct a Perpendicular Bisector of a Given Line Segment.How to Construct a Perpendicular Bisector.To do this requires constructing an equilateral triangle on the line segment.īefore moving on, review the construction of a perpendicular line. How to Construct a Perpendicular BisectorĪ perpendicular bisector is a line that meets a given line segment at a right angle and cuts the given line segment into two equal halves.Ĭonstructing such a line requires that we draw an equilateral triangle on the given line segment and then bisect the third vertex. Then, we extend the angle bisector so that it intersects the initial line. How to Construct a Perpendicular Bisector of a Given Line Segment We can then prove that this line will meet the given line at its center and form a right angle. We want to construct a line that meets this segment at a right angle and divides the given segment into two equal parts.įirst, we draw two circles with length AB. The first will have center A, while the second will have center B. Label the intersection of these circles as C and draw segments AC and BC. Then, we must bisect the angle ACB (how-to here). Call the intersection of the angle bisector and the line AB E. We can first prove that E is the center of AB by showing that AE=BE.ĪC=BC because they are both legs of an equilateral triangle, ACE=BCE because CE bisects ACB, and CE is equal to itself. Therefore, since the triangles, ACE and BCE, have two sides the same and the angle between those sides the same, the two triangles are congruent. This means that the third sides, namely AE and BE, are equivalent. Thus, E is the center of the segment AB, and CE bisects AB. Since the two resulting angles, CEA and CEB, are congruent and adjacent, they are right angles. How to Construct the Perpendicular Bisector of a Triangle Therefore, CE is also perpendicular to AB. ANSWERS TO GSP5 CONSTRUCTING PERPENDICULAR BISECTORS HOW TO Perpendicular bisectors are useful for finding the circumcenter of a triangle. That is, we use them to find a point inside a triangle that is equidistant from each of the vertices. To do this, we must construct a perpendicular bisector for each of the three legs of the triangle and draw it the whole way through the center of the triangle. The intersection of these three bisectors will be the circumcenter. This is true for any triangle, scalene, isosceles, or equilateral. In this section, we will go over common example problems involving the construction of perpendicular bisectors. Example 1įind the center of the given line segment.įirst, we construct an equilateral triangle on the line segment AB by creating two circles with radius AB. The first will have center A, and the second will have center B. If we construct lines from A and B to the intersection of the circles, C, we will construct an equilateral triangle ABC. Then, we can construct a second equilateral triangle by connecting A and B to the other intersection of the circles, D. Finally, if we connect CD and label the intersection of CD and AB as E, we will have found the center of AB. We know AE and BE are equal in length because the triangles ACE and BCE are congruent. This is because AC=BC, ACE=BCE, and CE are equal to themselves. Therefore, the triangles ACE and BCE are congruent, as are the sides AE and BE. Example 2Ĭonstruct a line perpendicular to the given line at point C. To do this, we first have to create a line segment that has C at its center. We can do this by constructing a circle with a radius equal to the shorter of AC and BC. Then, label the intersection of this circle and the line AB as D. Now we can proceed as if we were constructing a perpendicular bisector on the segment DB. In this case, we already know the center point, but that doesn’t change our procedure much. We still construct an equilateral triangle DBE. We know that EC is still perpendicular because we know DE=BE as they are both legs of an equilateral triangle and EDC=EBC because they are both angles of an equilateral triangle. We also know that DC=BC since they are both radii of the circle with center C and radius BC. ANSWERS TO GSP5 CONSTRUCTING PERPENDICULAR BISECTORS HOW TO.
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