Triangle Inequality Objective: –Students make conjectures about the measures of opposite sides and angles of triangles.
If one side of a triangle is longer than the other sides, then its opposite angle is longer than the other two angles. A B C Biggest Side is Opposite to Biggest Angle Medium Side is Opposite to Medium Angle Smallest Side is Opposite to Smallest Angle 4 9 m<B is greater than m<C 6
Converse is true also Biggest Angle Opposite ______ Medium Angle Opposite______ Smallest Angle Opposite______ Angle B > Angle A > Angle C So AC >BC > AB If one angle of a triangle is longer than the other angles, then its opposite side is longer than the other two sides. A B C ◦ 47 ◦
Triangle Inequality Objective: –determine whether the given triples are possible lengths of the sides of a triangle
A B C Triangle Inequality Theorem The sum of the lengths of any two sides of a triangle is greater than the length of the third side
Inequalities in One Triangle They have to be able to reach!!
Triangle Inequality Theorem AB + BC > AC AB + AC > BC AC + BC > AB A B C 4 9 6
Example: Determine if the following lengths are legs of triangles A)4, 9, ? 9 9 > 9 We choose the smallest two of the three sides and add them together. Comparing the sum to the third side: B) 9, 5, 5 Since the sum is not greater than the third side, this is not a triangle ? 9 10 > 9 Since the sum is greater than the third side, this is a triangle
Triangle Inequality Objective: –Solve for a range of possible lengths of a side of a triangle given the length of the other two sides.
A triangle has side lengths of 6 and 12; what are the possible lengths of the third side? 6 12 X = ? 1) = 18 2) 12 – 6 = 6 Therefore: 6 < X < 18
Examples Describe the possible lengths of the third side of the triangle given the lengths of the other two sides. 5 in 12 in 18 ft. 12 ft.10 yd. 23 yd.