(5.1) Midsegments of Triangles

1. (5.1) Midsegments of Triangles What will we be learning today? Use properties of midsegments to solve problems.

2. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Key Terms: A midsegment of a triangle is a segment connecting the midpoints of two sides.

3. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Example 1: Finding Lengths In XYZ, M, N and P are the midpoints. The Perimeter of MNP is 60. Find NP and YZ. Because the perimeter is 60, you can find NP. NP + MN + MP = 60 (Definition of Perimeter) NP + + = 60 NP + = 60 NP = x 24 M P 22 Y Z N

4. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Example 1: Use the Triangle Midsegment Theorem to find YZMP = of YZ Triangle Midsegment Thm.MP = 2424 = ½ YZ Substitute 24 for MP = YZMultiply both sides by 2 or the reciprocal of ½. x 24 M P 22 Y Z N

5. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Example 2: Identifying Parallel Segments Find the m<AMN and m<ANM. Line segments MN and BC are cut by transversal AB, so m<AMN and <B areangles.Line Segments MN and BC are parallel by theTheorem, so m<AMN is congruent to <B by the Postulate.m<AMN = 75 because congruent angles have the same measure. In triangle AMN, AM = ,so m<ANM = by the Triangle Theorem. m<ANM = by substitution. A corresponding Triangle Midsegment N M M Corresponding Angles AN m<AMN Isosceles 75O C 75 B

6. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Quick Check: • AB = 10 and CD = 28. Find EB, BC, and AC. A E B C D

7. Theorem 5-1: Triangle Midsegment TheoremIf a segment joins the midpoints of two sides of a triangle, then the segment is parallel to the third side, and is half its length Quick Check: 2. Critical Thinking Find the m<VUZ. Justify your answers. X 65O U Z Y V

8. HOMEWORK (5.4) Pgs. 325-363; 18- 26,27,49

9. (5.2) Bisectors in Triangles What will we be learning today? Use properties of perpendicular bisectors and angle bisectors.

10. Theorems Theorem 5-2: Perpendicular Bisector Thm.If a point is on the perpendicular bisector of a segment, then it is equidistant form the endpoints of the segment. Theorem 5-3: Converse of the Perpendicular Bisector Thm.If a point is equidistant from the endpoints of a segment, then it is on the perpendicular bisector of the segment.

11. Theorems Theorem 5-4: Angle Bisector Thm.If a point is on the bisector of an angle, then it is equidistant from the sides of the angle. Theorem 5-5: Converse of the Angle Bisector Thm.If a point in the interior of an angle is equidistant from the sides of the angle, then it is on the angle bisector.

12. Key Concepts The distance from a point to a line is the length of the perpendicular segment from the point to the line. Example: D is 3 in. from line AB and line AC C D 3 A B

13. Example Using the Angle Bisector Thm. Find x, FB and FD in the diagram at the right. Show steps to find x, FB and FD: FD = Angle Bisector Thm. 7x – 35 = 2x + 5 A 2x + 5 B F 7x - 35 C D E

14. Quick Check a. According to the diagram, how far is K from ray EH? From ray ED? 2xO D E C (X + 20)O K 10 H

15. Quick Check b. What can you conclude about ray EK? 2xO D E C (X + 20)O K 10 H

16. Quick Check c. Find the value of x. 2xO D E C (X + 20)O K 10 H

17. Quick Check d. Find m<DEH. 2xO D E C (X + 20)O K 10 H

18. HOMEWORK (5.2) Pgs. 267-269; 1-4, 6, 8-26, 28, 29, 40, 43, 46, 48