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GBK Geometry. Jordan Johnson. Today’s plan. Greeting Warm-up Midsegment Conjectures / Proofs Homework / Questions Clean-up. Review Question. What is the definition of midsegment ?. Midsegment Conjectures. DE║AC ? DE = AC ⁄ 2 ? DE = DA + EC ⁄ 2 ? A ADEC = 3A DBE ?.
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GBK Geometry Jordan Johnson
Today’s plan • Greeting • Warm-up • Midsegment Conjectures / Proofs • Homework / Questions • Clean-up
Review Question What is the definition ofmidsegment ?
Midsegment Conjectures • DE║AC ? • DE = AC⁄2 ? • DE = DA + EC⁄2 ? • AADEC = 3ADBE ?
The Midsegment Theorem • A midsegment of a triangle is parallel to, and half the length of, the side it doesn’t intersect. • If DE is a midsegment of ABC, then DE = AC⁄2 and DE║AC.
The Midsegment Theorem:Proof Strategy • (Theorem 37): A midsegment of a triangle is parallel to the third side and half its length. • Hints: • Draw line BC and choose P on it so that BC = CP. • Prove that BBPC is a parallelogram. • Use parallelogram theorems.
Tasks • Work on midsegment proofs / conjectures. • Asg #58: From Ch. 9, Lesson 1 (p. 341-343), do: • Set I Exercises 1-24 • Set II Exercises 25-34, 44-45. • Due Thursday, 3/14. • Read Chapter 9, Lesson 2 (pp. 345-348), and do: • Set I Exercises 5-6, 11-27. • Set II Exercises 28-29, 53-57. • Bonus: Set III. • Due Friday, 3/15.
Clean-up / Reminders • Pick up all trash / items. • Push in chairs (at front and back tables). • See you tomorrow!