1. Inequalities in Two Triangles
5-6
Inequalities in Two Triangles
Warm Up
Lesson Presentation
Lesson Quiz
Holt McDougal Geometry
Holt Geometry

2. Warm Up 1. Write the angles in order from smallest to largest.
2. The lengths of two sides of a triangle are 12 cm and 9 cm. Find the range of possible lengths for the third side.
X, Z, Y
3 cm < s < 21 cm

3. Objective
Apply inequalities in two triangles.

5. Example 1A: Using the Hinge Theorem and Its Converse
Compare mBAC and mDAC.
Compare the side lengths in ∆ABC and ∆ADC.
AB = AD AC = AC BC > DC
By the Converse of the Hinge Theorem, mBAC > mDAC.

6. Example 1B: Using the Hinge Theorem and Its Converse
Compare EF and FG.
Compare the sides and angles in ∆EFH angles in ∆GFH.
mGHF = 180° – 82° = 98°
EH = GH FH = FH mEHF < mGHF
By the Hinge Theorem, EF < GF.

7. Check It Out! Example 2A
Compare mEGH and mEGF.
Compare the side lengths in ∆EGH and ∆EGF.
FG = HG EG = EG EF > EH
By the Converse of the Hinge Theorem, mEGH < mEGF.

8. Check It Out! Example 2B
Compare BC and AB.
Compare the side lengths in ∆ABD and ∆CBD.
AD = DC BD = BD mADB < mCDB.
By the Hinge Theorem, BC > AB.

9. Example NOT ON NOTES!!!
Find the range of values for k.
Step 1 Compare the side lengths in ∆MLN and ∆PLN.
LN = LN LM = LP MN > PN
By the Converse of the Hinge Theorem, mMLN > mPLN.
5k – 12 < 38
Substitute the given values.
k < 10
Add 12 to both sides and divide by 5.

10. Example- Continued
Step 2 Since PLN is in a triangle, mPLN > 0°.
5k – 12 > 0
Substitute the given values.
k > 2.4
Add 12 to both sides and divide by 5.
Step 3 Combine the two inequalities.
The range of values for k is 2.4 < k < 10.

11. Example NOT ON NOTES: Travel Application- Short Response
John and Luke leave school at the same time. John rides his bike 3 blocks west and then 4 blocks north. Luke rides 4 blocks east and then 3 blocks at a bearing of N 10º E. Who is farther from school? Explain.

12. Example- Continued
The distances of 3 blocks and 4 blocks are the same in both triangles.
The angle formed by John’s route (90º) is smaller than the angle formed by Luke’s route (100º). So Luke is farther from school than John by the Hinge Theorem.

13. Check It Out! Example NOT ON NOTES
When the swing ride is at full speed, the chairs are farthest from the base of the swing tower. What can you conclude about the angles of the swings at full speed versus low speed? Explain.
The  of the swing at full speed is greater than the  at low speed because the length of the triangle on the opposite side is the greatest at full swing.

14. Lesson Quiz: Part I
1. Compare mABC and mDEF.
2. Compare PS and QR.
mABC > mDEF
PS < QR

15. Lesson Quiz: Part II
3. Find the range of values for z.
–3 < z < 7