Inequalities in Triangles
Definition of Inequality For any real numbers a and b, a > b if and only if there is a positive number c such that a = b + c.
Exterior Angle Inequality The measure of an exterior angle of a triangle is greater than the measure of either of its corresponding remote interior angles.
Examples Find all measures less than angle 7.
Examples Find all measures greater than angle 6.
Examples Find all measures greater than angle 1.
Examples Find all measures greater than angle 8.
Angle-Side Relationships If one side of a triangle is longer than another side, then the angle opposite the longer side has a greater measure than the angle opposite the shorter side.
Examples List the angles of PQR in order from smallest to largest.
Examples List the angles of PQR in order from smallest to largest.
Angle-Side Relationships If one angle of a triangle has a greater measure than another angle, then the side opposite the greater angle is longer than the side opposite the lesser angle.
Examples List the sides of FGH in order from shortest to longest.
Examples List the sides of WXY in order from shortest to longest.
Triangle Inequality Theorem The sum of the lengths of any two sides of a triangle must be greater than the length of the third side.
Examples Is it possible to form a triangle with the given side lengths? If not, explain why not. 8, 15, 17
Examples Is it possible to form a triangle with the given side lengths? If not, explain why not. 6, 8, 14
Examples Is it possible to form a triangle with the given side lengths? If not, explain why not. 15, 16, 30
Examples Is it possible to form a triangle with the given side lengths? If not, explain why not. 2, 8, 11
Triangle Inequality Theorem When the lengths of two sides of a triangle are known, the third side can be any length in a range of values. You can use the Triangle Inequality Theorem to determine the range of possible lengths for the third side.
Triangle Inequality Theorem To do this, find the sum and the difference of the two known sides. The sum provides the upper limit and the difference provides the lower limit. 13 + 9 = 22 13 – 9 = 4 4 < n < 22