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Understand triangle inequalities with Theorems 5.10, 5.11, and 5.12, learn about the Exterior Angle Inequality and Triangle Inequality Theorem, and discover examples showing application in triangle sides and angles relationships.
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Chapter 5Section 5.5 Inequalities in a triangle
-3 -3 +9 -2x -10 -10 +9 -2x -1 2 -1 2 Don’t forget to change it! 3 < 2x - 9 x < 11 2 > -x 12 < 2x -2<x 6<x
Compare Sides to Order Angles C B A Theorem Theorem 5.10 If one side of a triangle is longer than another side, then the angle opposite the longer side is larger than the angle opposite the shorter side. mA > mB > mC CB > CA > AB
Compare Angles to Order Sides R P Q Theorem Theorem 5.11 If one Angle of a triangle is larger than another angle, then the side opposite the larger angle is longer than the side opposite the smaller angle. mP > mQ > mR QR > PR > PQ
mM > mK > mL KL > LM > KM
mM > mO > mN ON > MN > OM
mB > mA > mC AC > BC> AB
EG > GF > EF mF > mE > mG
mJ > mI > mH HI > HJ > IJ
LM > KM > KL mK > mL > mM
In ABC CB > AB > AC In CBD BD > CD > CB Thus BD > CD > CB > AB > AC
In LKM LM > KL > KM In LMN MN > LN > LM Thus MN > LN > LM > LN > LM
Inequalities in a triangle R P Q T Theorem Theorem 5.12 Exterior Angle Inequality The measure of an exterior angle of a triangle is greater than the measure of the two nonadjacent interior angles. TQR is an exterior angle of QRP mTQR > mR And mTQR > mP
Inequalities in a triangle Theorem Theorem 5.13 Triangle Inequality The sum of the lengths of any two sides of a triangle is greater than the length of the third side. AB + BC > AC AB + AC > BC BC + AC > AB
The sum of any two sides must be greater than the third side! YZ + XY > XZ XZ + XY > YZ XZ + YZ > XY 2 + XY > 3 3 + XY > 2 2 + 3 > XY XY > 1 5 > XY XY > -1 5 > XY > 1
The sum of any two sides must be greater than the third side! YZ + XY > XZ XZ + XY > YZ XZ + YZ > XY 8 + XY > 10 10 + XY > 8 8 + 10 > XY XY > 2 18 > XY XY > -2 18 > XY > 2
CC 60 AF 40 DS 60 + x > 40 60 + 40 > x x + 40 > 60 100 > x x > -20 x > 20 x 100 > x > 20 No, the distance must be less than 100 miles