1. Chapter 5: Relationships in Triangles

2. Bisectors, Medians, and Altitudes
Lesson 5.1
Bisectors, Medians, and Altitudes

3. Foldable
Frayer: Fold paper in half both width and length wise. While folded, fold the corner where all creases meet. Then open.

4. Perpendicular Bisector ( bisector)
A line, segment, or ray that passes through the midpoint of the side and is perpendicular to the side.
Does not need to pass through a vertex
Any point on a perpendicular bisector is equidistant from the endpoints
Any point equidistant from the endpoints is on the perpendicular bisector
Circumcenter: the point where 3 perpendicular bisectors meet
Is equidistant from all vertices of the triangle

5. Perpendicular Bisector
CF, BE, and AD are perpendicular bisectors
OB, OC and OA are congruent
There are always 3 perpendicular bisectors for a triangle F E O C B D

6. Median
A segment that goes from a vertex of the triangle to the midpoint of the opposite side
Centroid: is the point where three medians intersect
The center of gravity for the triangle
The small part of the median is 1/3 of the whole median
2 x small = big
1/3 median = small
2/3 median = big

7. Median L LQ, MP, and NO are medians of triangle LMN 2 x PX = MX
2 x OX = NX
2 x QX = LX
There are always 3 medians per triangle O P X N M Q

8. Angle Bisector ( bisector)
A line, segment or ray that passes through the middle of the angle it begins in and extends to the opposite side
Any point on the angle bisector is equidistant from the sides of the triangle
Any point equidistant from both sides is on the angle bisector
Incenter: the point where three angle bisectors intersect
Equidistant from all sides of the triangle

9. Angle bisector I L M A H J K X U T W Z V Y
IK, HM, and JL are angle bisectors:
Angles LIA and MIA, angles MJA and KJA, and angles KHA and LHA are congruent to their partner angle.
LA, MA, and KA are congruent.
ZW is an angle bisector
TU and TV are congruent
There are always 3 angle bisectors per triangle L M A H J K X U T W Z V Y

10. Altitude
A segment that goes from a vertex of the triangle to the opposite side and is perpendicular to that side
Orthocenter: the point where three altitudes intersect

11. Altitude SU, VW, and TY are altitudes of the triangle
R is the orthocenter
An altitude of a triangle could be outside of the triangle.
There are always 3 altitudes per triangle S Y W R V T U

12. Inequalities and Triangles
Lesson 5.2
Inequalities and Triangles

13. Foldable
Fold the paper into three sections (burrito fold) Then fold the top edge down about ½ and inch
Unfold the paper and in the top small rectangles label each column…

14. Exterior Angle Inequality Inequality with Sides Inequality with Angles
* Remote Int. + Remote Int. = Exterior Angle
The exterior angle is greater than either of the remote interior angles by themselves
rem. Int. < ext.
Ex:
The biggest side is across from the biggest angle
The smallest side is across from the smallest angle
-The biggest angle is across from the biggest side/ the smallest angle is across from the smallest side

15. Lesson 5.3
Indirect Proof

16. Steps to Completing and Indirect Proof:
Assume that the conclusion is false
Then _______________ (show that the assumption leads to a contradiction) This contradicts the given information that ________________.
Therefore, __________________ (rewrite the conclusion) must be true.

17. Example Indirect Proof
Given: 5x < 25
Prove: x < 5
Assume that x
Then, x = 6. So, 5(6) < 25
30 < 25
This contradicts the given information that
5x < 25.
3. Therefore, x < 5 must be true.

18. Example Indirect Proof
Given: m is not parallel to n
Prove: m m 2
Assume that m = m
Then, angle 3 and angle 2 are alternate interior angles.
When alternate interior angles are congruent then the lines that make them are parallel.
That means m and n are parallel.
This contradicts the given information that m is not parallel to n.
3. Therefore, m m must be true

19. The Triangle Inequality
Lesson 5.4
The Triangle Inequality

20. Triangle Inequality Theorem
The sum of the lengths of any two sides of a triangle is greater than the length of the third side

21. Triangle Inequality Theorem Problems
Determine if the measures given could be the sides of a triangle.
16, 17, 19
= 33 yes, the sum of the two smallest sides is larger than the third side
6, 9, 15
6 + 9 = 15 no, the sum of the two smallest sides is equal to the other side so it cannot be a triangle
Find the range for the measure of the third side given the measures of two sides.
7.5 and 12.1
< x <
4.6 < x < 19.6
9 and 41
41-9 < x <
32 < x < 50

22. Inequalities Involving Two Triangles
Lesson 5.5
Inequalities Involving Two Triangles

23. On the other side of the foldable from Lesson 2 (3 column chart)
SAS Inequality Theorem
SSS Inequality Theorem
Examples:
(Hinge Theorem)
When 2 sides of a triangle are congruent to 2 sides of another triangle, and the included angle of one triangle is greater than the included angle of the other triangle…
Then, the side opposite the larger angle is larger than the side opposite the smaller angle
When 2 sides of a triangle are congruent to 2 sides of another triangle, and the 3rd side of a triangle is greater than the 3rd side of the other triangle…
Then, the angle opposite the larger side is larger than the angle opposite the smaller side
Ex: