Show that BE and CD are parallel 13.5 A. 12 E 18

Elementary Geometry For College Students, 7e
7th Edition
ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
SectionP.CT: Test
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**Title: Proving Parallel Lines in Triangles**

**Objective:**
Show that \( BE \) and \( CD \) are parallel.

**Diagram Description:**
The image depicts a triangle \( ABC \). The point \( D \) is on the extension of side \( AB \) such that \( AC \) and \( CD \) form the triangle \( ACD \). The points \( B \) and \( E \) are marked on sides \( AC \) and \( AD \) respectively. \( BE \) and \( CD \) are two line segments drawn inside the triangle.

**Given Measurements:**
- \( AB = 12 \)
- \( AE = 12 \)
- \( AD = 18 \)
- \( BE \) is perpendicular to \( AD \).
- \( CD \) is perpendicular to \( AD \).
- \( AC = 13.5 \)
- \( CB = 9 \)
  
**Explanation:**
To prove that \( BE \parallel CD \), we can use the properties of similar triangles and parallel lines.

1. Identify triangles \( ABE \) and \( CDE \):
   - Both triangles share the angle \( A \).
   - Both contain the right angles at \( BE \) and \( CD \) respectively.

2. Use the intercept theorem (or Thales' theorem):
   - Triangles \( ABE \) and \( CDE \) are similar by AA similarity criterion (since both have a right angle and share angle \( A \)).
   
3. Apply the theorem proportionally:
   - In similar triangles, corresponding sides are proportional, so:
   
     \[
     \frac{AB}{AC} = \frac{AE}{AD}
     \]
     
     Substituting the given values:
     
     \[
     \frac{12}{13.5} = \frac{12}{18}
     \]
     
     Simplify both fractions:
     
     \[
     \frac{4}{4.5} = \frac{2}{3}
     \]
     
     \[
     \frac{4}{4.5} = \frac{2}{3}
     \]
     
     This equality confirms that the triangles are cut by two parallel lines because corresponding sides are proportional.
     
Therefore, since \( \frac{AB}{AC} = \frac{AE}{AD} \), lines \( BE \) and \( CD \
Transcribed Image Text:**Title: Proving Parallel Lines in Triangles** **Objective:** Show that \( BE \) and \( CD \) are parallel. **Diagram Description:** The image depicts a triangle \( ABC \). The point \( D \) is on the extension of side \( AB \) such that \( AC \) and \( CD \) form the triangle \( ACD \). The points \( B \) and \( E \) are marked on sides \( AC \) and \( AD \) respectively. \( BE \) and \( CD \) are two line segments drawn inside the triangle. **Given Measurements:** - \( AB = 12 \) - \( AE = 12 \) - \( AD = 18 \) - \( BE \) is perpendicular to \( AD \). - \( CD \) is perpendicular to \( AD \). - \( AC = 13.5 \) - \( CB = 9 \) **Explanation:** To prove that \( BE \parallel CD \), we can use the properties of similar triangles and parallel lines. 1. Identify triangles \( ABE \) and \( CDE \): - Both triangles share the angle \( A \). - Both contain the right angles at \( BE \) and \( CD \) respectively. 2. Use the intercept theorem (or Thales' theorem): - Triangles \( ABE \) and \( CDE \) are similar by AA similarity criterion (since both have a right angle and share angle \( A \)). 3. Apply the theorem proportionally: - In similar triangles, corresponding sides are proportional, so: \[ \frac{AB}{AC} = \frac{AE}{AD} \] Substituting the given values: \[ \frac{12}{13.5} = \frac{12}{18} \] Simplify both fractions: \[ \frac{4}{4.5} = \frac{2}{3} \] \[ \frac{4}{4.5} = \frac{2}{3} \] This equality confirms that the triangles are cut by two parallel lines because corresponding sides are proportional. Therefore, since \( \frac{AB}{AC} = \frac{AE}{AD} \), lines \( BE \) and \( CD \
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