### Problem Statement In the given diagram, two triangles are shown: ΔABC and ΔCDE. Here, AB is 3 units, BC is 4.5 units, DE is \( x \) units, and CD is \( x + 6 \) units. The lengths marked for these line segments are given as: - \( AB = 3 \) - \( BC = 4.5 \) - \( DE = x \) - \( CD = x + 6 \) The triangles share a common vertex at C, and lines EA and EB are red marked indicating they are congruent. Your goal is to **find the length of CD**. ### Steps to Solve 1. **Recognize Similar Triangles**: From the diagram assumptions, ΔABC is similar to ΔCDE by AA similarity (both triangles share ∠EAD and ∠ACD). 2. **Set Up Proportions**: Since the triangles are similar, the ratios of corresponding sides in similar triangles are equal. \[ \frac{AB}{DE} = \frac{BC}{CD} \] Substitute the given lengths: \[ \frac{3}{x} = \frac{4.5}{x + 6} \] 3. **Cross-Multiply to Solve for \( x \)**: \[ 3(x + 6) = 4.5x \] Simplify the equation. \[ 3x + 18 = 4.5x \] \[ 18 = 4.5x - 3x \] \[ 18 = 1.5x \] \[ x = 12 \] 4. **Find CD**: Substitute the value of \( x \) to find the length of CD. \[ CD = x + 6 = 12 + 6 = 18 \] ### Conclusion The length of CD is \( \boxed{18} \) units.

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
Problem 1CT
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### Problem Statement

In the given diagram, two triangles are shown: ΔABC and ΔCDE. Here, AB is 3 units, BC is 4.5 units, DE is \( x \) units, and CD is \( x + 6 \) units. The lengths marked for these line segments are given as:

- \( AB = 3 \)
- \( BC = 4.5 \)
- \( DE = x \)
- \( CD = x + 6 \)

The triangles share a common vertex at C, and lines EA and EB are red marked indicating they are congruent.

Your goal is to **find the length of CD**.

### Steps to Solve

1. **Recognize Similar Triangles**: 
   From the diagram assumptions, ΔABC is similar to ΔCDE by AA similarity (both triangles share ∠EAD and ∠ACD).
   
2. **Set Up Proportions**: 
   Since the triangles are similar, the ratios of corresponding sides in similar triangles are equal.
   \[
   \frac{AB}{DE} = \frac{BC}{CD}
   \]
   Substitute the given lengths:
   \[
   \frac{3}{x} = \frac{4.5}{x + 6}
   \]

3. **Cross-Multiply to Solve for \( x \)**:
   \[
   3(x + 6) = 4.5x
   \]
   Simplify the equation.
   \[
   3x + 18 = 4.5x
   \]
   \[
   18 = 4.5x - 3x
   \]
   \[
   18 = 1.5x
   \]
   \[
   x = 12
   \]

4. **Find CD**:
   Substitute the value of \( x \) to find the length of CD.
   \[
   CD = x + 6 = 12 + 6 = 18
   \]

### Conclusion

The length of CD is \( \boxed{18} \) units.
Transcribed Image Text:### Problem Statement In the given diagram, two triangles are shown: ΔABC and ΔCDE. Here, AB is 3 units, BC is 4.5 units, DE is \( x \) units, and CD is \( x + 6 \) units. The lengths marked for these line segments are given as: - \( AB = 3 \) - \( BC = 4.5 \) - \( DE = x \) - \( CD = x + 6 \) The triangles share a common vertex at C, and lines EA and EB are red marked indicating they are congruent. Your goal is to **find the length of CD**. ### Steps to Solve 1. **Recognize Similar Triangles**: From the diagram assumptions, ΔABC is similar to ΔCDE by AA similarity (both triangles share ∠EAD and ∠ACD). 2. **Set Up Proportions**: Since the triangles are similar, the ratios of corresponding sides in similar triangles are equal. \[ \frac{AB}{DE} = \frac{BC}{CD} \] Substitute the given lengths: \[ \frac{3}{x} = \frac{4.5}{x + 6} \] 3. **Cross-Multiply to Solve for \( x \)**: \[ 3(x + 6) = 4.5x \] Simplify the equation. \[ 3x + 18 = 4.5x \] \[ 18 = 4.5x - 3x \] \[ 18 = 1.5x \] \[ x = 12 \] 4. **Find CD**: Substitute the value of \( x \) to find the length of CD. \[ CD = x + 6 = 12 + 6 = 18 \] ### Conclusion The length of CD is \( \boxed{18} \) units.
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