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Special Segments of Similar Triangles and Triangle Angle Bisector Theorem

This lesson covers the theorems and examples related to special segments of similar triangles and the triangle angle bisector theorem. Learn how to solve problems using similar triangles and apply the Triangle Angle Bisector Theorem.

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Special Segments of Similar Triangles and Triangle Angle Bisector Theorem

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  1. Splash Screen

  2. Five-Minute Check (over Lesson 7–4) NGSSS Then/Now Theorems: Special Segments of Similar Triangles Proof: Theorem 7.8 Example 1: Use Special Segments in Similar Triangles Example 2: Real-World Example: Use Similar Triangles to Solve Problems Theorem 7.11: Triangle Angle Bisector Example 3: Use the Triangle Angle Bisector Theorem Lesson Menu

  3. A B C D If QT = 5, TR = 4, and US = 6, find QU. A. 5.5 B. 6 C. 7 D. 7.5 5-Minute Check 1

  4. A B C D If TQ = x + 1, TR = x – 1, QU = 10, and QS = 15, solve for x. A. 2 B. 3 C. 4.4 D. 5.6 5-Minute Check 2

  5. A B C D If AB = 5, ED = 8, BC = 11, and DC = x – 2, find x sothat BD || AE. ___ ___ A. 10 B. 15.4 C. 19.6 D. 21.3 5-Minute Check 3

  6. A B If AB = 4, BC = 7, ED = 5, and EC = 13.75, determinewhether BD || AE. ___ ___ A. yes B. no 5-Minute Check 4

  7. A B C D In the diagram, 1st Street is parallel to 3rd Street and 5th Street. Find the distance from 3rd Street to 5th Street if you are traveling on 4th Street. A. 1.0 mi B. 2.2 mi C. 2.9 mi D. 3.1 mi 5-Minute Check 5

  8. MA.912.G.2.3Use properties of congruent and similar polygons to solve mathematical or real-world problems. MA.912.G.4.6 Prove that triangles are congruent or similar and use the concept of corresponding parts of congruent triangles. Also addresses MA.912.G.4.4. NGSSS

  9. You learned that corresponding sides of similar polygons are proportional. (Lesson 7–2) • Recognize and use proportional relationships of corresponding angle bisectors, altitudes, and medians of similar triangles. • Use the Triangle Bisector Theorem. Then/Now

  10. Concept

  11. Concept

  12. MK and TR are corresponding medians and LJ and SQ are corresponding sides. JL = 2x and QS = 2(5) or 10. Use Special Segments in Similar Triangles In the figure, ΔLJK ~ ΔSQR. Find the value of x. Example 1

  13. ~Δ have corr. medians proportional to the corr. sides. Use Special Segments in Similar Triangles Substitution 12 ● 10 = 8 ● 2x Cross Products Property 120 = 16x Simplify. 7.5 = x Divide each side by 16. Answer:x = 7.5 Example 1

  14. A B C D In the figure, ΔABC ~ ΔFGH. Find the value of x. A. 7 B. 14 C. 18 D. 31.5 Example 1

  15. Use Similar Triangles to Solve Problems ESTIMATING DISTANCESanjay’s arm is about 9 times longer than the distance between his eyes. He sights a statue across the park that is 10 feet wide. If the statue appears to move 4 widths when he switches eyes, estimate the distance from Sanjay’s thumb to the statue. Example 2

  16. We assume if Sanjay’s thumb is straight out in front of him, then PC is an altitude of ΔABC. Likewise, QC is the corresponding altitude. We assume that AB || DF. Use Similar Triangles to Solve Problems Understand Make a diagram of the situation labeling the given distance you need to find as x. Also, label the vertices of the triangles formed. Example 2

  17. Plan Since AB || DF, BAC DFC and CBA CDF by the Alternate Interior Angles Theorem. Therefore ΔABC ~ ΔFDC by AA Similarity. Write a proportion and solve for x. Theorem 7.8 Substitution Simplify. Use Similar Triangles to Solve Problems Solve Example 2

  18. Use Similar Triangles to Solve Problems 9 ● 40 = x ● 1 Cross Products Property 360 = x Simplify. Answer: So the estimated distance to the statue is 360 feet. Check The ratio of Sanjay’s arm length to the width between his eyes is 9 to 1. The ratio of the distance to the statue to the distance the image of the statue jumped is 40 to 360 or 9 to 1. Example 2

  19. A B C D Use the information from Example 2.Suppose Sanjay turns around and sees a sailboat in the lake that is 12 feet wide. If the sailboat appears to move 4 widths when he switches eyes, estimate the distance from Sanjay’s thumb to the sailboat. A. 324 feet B. 432 feet C. 448 feet D. 512 feet Example 2

  20. Concept

  21. Use the Triangle Angle Bisector Theorem Find x. Since the segment is an angle bisector of the triangle, the Angle Bisector Theorem can be used to write a proportion. Example 3

  22. Use the Triangle Angle Bisector Theorem Triangle Angle Bisector Theorem • 9x = (15)(6) Cross Products Property • 9x = 90 Simplify. • x = 10 Divide each side by 9. Answer:x = 10 Example 3

  23. A B C D Find n. A. 10 B. 15 C. 20 D. 25 Example 3

  24. End of the Lesson

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