The Longest Side
Part of the Triangles section of Coddy's Geometry journey. Lesson 5 of 71.
In any triangle, the longest side is opposite the largest angle, and the shortest side is opposite the smallest angle. In the figure, the angles are 60°, 40° and 80°. Side c is opposite the 80° angle at C, so c is the longest side. Side b is opposite the 40° angle at B, so b is the shortest side.
The largest angle is opposite the longest side
The rule works in both directions. If you know the order of the angles, you know the order of the sides. If you know the order of the sides, you know the order of the angles. Equal angles are opposite equal sides. In a right triangle, the right angle is larger than either of the other two angles, so the side opposite it, the hypotenuse, is the longest side.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Triangles
1Sides and Names
Three Sides, Three CornersSorting by SidesNaming by AnglesTicks into EquationsThe Longest SideRecap: Sorting Triangles2The Triangle Inequality
Can Three Sticks Meet?Exactly ReachingHow Short Can It Be?How Long Can It Be?The Range of the Third SideThe FormulaWhole-Number SidesRecap: The Third Side5The Hypotenuse
Squares on the SidesFinding the HypotenusePythagorean TriplesWhen It Is Not WholeSimplifying the RootRecap: The Hypotenuse8Special Right Triangles
The 45-45-90 TriangleLegs from the HypotenuseThe 30-60-90 TriangleAll Three SidesWhich Triangle Is It?Recap: Special Triangles11Mixing Area and Pythagoras
Height of an IsoscelesArea from the HeightThe Equilateral TriangleRight Triangle PerimeterRecap: Two Tools3Perimeter
Around the EdgeA Missing SideIsosceles PerimeterEquilateral PerimeterSides as ExpressionsWrite the PerimeterRecap: Around the Edge6Finding a Leg
Working BackwardsThe LadderWhich Side Is c?A Leg That Is Not WholeRecap: Finding a Leg