QUESTION IMAGE
Question
lenny wrote a paragraph proof of the perpendicular bisector theorem. what mistake did lenny make in his proof?
\\( \overline { h k } \\) is a perpendicular bisector of \\( \overline { i j } \\), and \\( l \\) is the midpoint of \\( \overline { i j } \\). \\( m \\) is a point on the perpendicular bisector, \\( \overline { h k } \\). by the definition of a perpendicular bisector, i know that \\( \overline { i m } \cong \overline { j m } \\). by the definition of a perpendicular bisector, i also know that \\( \angle m l i \\) and \\( \angle m l j \\) are right angles. \\( \angle m l i \cong \angle m l j \\) because of the right angle congruence theorem. i can also say that \\( \overline { m l } \cong \overline { m l } \\) by the reflexive property of congruence. with this information, i know that \\( \triangle m l i \cong \triangle m l j \\) by the sas congruence theorem. since the triangles are congruent, the cpctc theorem allows me to know that \\( \overline { i l } \cong \overline { j l } \\). knowing that these segments are congruent proves the perpendicular bisector theorem.
(1 point)
the sas congruence theorem tells you that \\( \triangle m l i \cong \triangle j l m \\), not that \\( \triangle m l i \cong \triangle m l j \\)
lenny did not make a mistake. his proof is correct.
the definition of a perpendicular bisector tells you that \\( \overline { i l } \cong \overline { j l } \\), not that \\( \overline { i m } \cong \overline { j m } \\)
the definition of a perpendicular bisector tells you that \\( \angle l m i \\) and \\( \angle l m j \\) are right angles, not that \\( \angle m l i \\) and \\( \angle m l j \\) are right angles
Step1: Recall the definition of perpendicular bisector
The perpendicular bisector of a segment is a line that is perpendicular to the segment and passes through its mid - point. By the definition of a perpendicular bisector, if \(HK\) is the perpendicular bisector of \(IJ\) and \(L\) is the mid - point of \(IJ\), then \(IL = JL\) (i.e., \(\overline{IL}\cong\overline{JL}\)).
Step2: Analyze the incorrect statement
The statement “By the definition of a perpendicular bisector, I know that \(\overline{IM}\cong\overline{JM}\)” is wrong. The property \(\overline{IM}\cong\overline{JM}\) (where \(M\) is a point on the perpendicular bisector \(HK\)) is the conclusion of the Perpendicular Bisector Theorem (a point on the perpendicular bisector of a segment is equidistant from the endpoints of the segment), not the definition. The definition only gives the congruence of the two sub - segments (\(\overline{IL}\) and \(\overline{JL}\)) of the bisected segment \(IJ\) by its mid - point \(L\).
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The definition of a perpendicular bisector tells you that \(\overline{IL}\cong\overline{JL}\), not that \(\overline{IM}\cong\overline{JM}\)