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Question
your friend asks you for help on a geometry exercise. your friends paper is shown to the right. what error did your friend make? explain
choose the correct answer below
a. the asa postulate cannot be used to prove the congruence of the two triangles as shown because the included sides between the two pairs of congruent angles are not marked as congruent in both triangles
b. your friends paper does not name the triangles correctly for them to be congruent.
c. your friends paper shows that the sas postulate should be used to show congruence because a pair of congruent angles is included between two pairs of congruent sides.
d. the asa postulate cannot be used to prove the congruence of the two triangles as shown because the triangles do not have two pairs of congruent angles.
To determine the error, we analyze each option:
- Option A: ASA (Angle - Side - Angle) requires two angles and the included side to be congruent. In the given triangles, the included sides between the congruent angles are not marked as congruent, so ASA can't be used. This is a valid point.
- Option B: Naming triangles incorrectly doesn't relate to the congruence proof error here.
- Option C: The markings don't suggest SAS (two sides and included angle) as there's no indication of two pairs of congruent sides with an included angle.
- Option D: The triangles do have two pairs of congruent angles (marked angles), so this is incorrect.
Also, for congruent triangles named $\triangle LMN\cong\triangle QRS$, the order of vertices should correspond to congruent parts. In $\triangle LMN$, the angles at $L$ and $N$ are marked, and in $\triangle QRS$, the angles at $Q$ and $S$ are marked. The correct naming should match the congruent angles and sides. So the friend didn't name the triangles correctly for congruence (matching corresponding parts), which is what Option B is about? Wait, no, let's re - evaluate.
Wait, the ASA postulate: Let's look at the triangles. In $\triangle LMN$, we have angle at $L$, side $LN$, angle at $N$. In $\triangle QRS$, we have angle at $Q$, side $QS$, angle at $S$? No, the markings: one triangle has a mark on angle $L$ and angle $N$, and the other has a mark on angle $Q$ and angle $S$, and a mark on a side (but not the included side). Wait, the key is the naming of the triangles. For two triangles to be congruent by ASA (or any postulate), the order of the vertices must correspond to the congruent parts. In $\triangle LMN$ and $\triangle QRS$, the correspondence of vertices is not correct. So Option B says "Your friend’s paper does not name the triangles correctly for them to be congruent." This is the error. Let's check the other options again.
Option A: The included side - in ASA, the side between the two angles. In $\triangle LMN$, the side between $\angle L$ and $\angle N$ is $LN$. In $\triangle QRS$, the side between $\angle Q$ and $\angle S$ is $QS$. But the problem is the naming of the triangles. Wait, maybe I made a mistake earlier. Let's re - examine the triangle markings.
Looking at the triangles: $\triangle LMN$ has angles at $L$ and $N$ marked (let's say congruent to angles at $Q$ and $S$ in $\triangle QRS$) and a side (maybe $LM$ and $RQ$? No, the markings: one triangle has a mark on a side (not the included side) and two angles, the other has a mark on a side (not the included side) and two angles. Wait, the correct answer is B? Wait, no, let's check the options again.
Wait, the ASA postulate: If we have two triangles, for ASA, we need two angles and the included side. But also, the naming of the triangles must be in the order of corresponding parts. So if $\triangle LMN\cong\triangle QRS$, then $\angle L\cong\angle Q$, $\angle M\cong\angle R$, $\angle N\cong\angle S$ and sides $LM\cong QR$, $MN\cong RS$, $LN\cong QS$. But in the diagram, the marked angles in $\triangle LMN$ are at $L$ and $N$, and in $\triangle QRS$ are at $Q$ and $S$. The vertex $M$ in $\triangle LMN$ should correspond to vertex $R$ in $\triangle QRS$, but the naming $\triangle LMN\cong\triangle QRS$ does not match the corresponding angles (since $\angle M$ and $\angle R$ are not the marked angles). So the triangles are not named correctly for congruence, which is Option B.
Wait, but let's check Option A again. The ASA postulate requires the included side (the side between the two angles) to be congruent. In $\triangle LMN$,…
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B. Your friend’s paper does not name the triangles correctly for them to be congruent.