Equilateral Perimeter
Part of the Triangles section of Coddy's Geometry journey. Lesson 18 of 71.
An equilateral triangle has three equal sides, so its perimeter is three times the side: P = 3s. If the perimeter is 27, one division gives the side:
Three equal sides of s
3s = 27
s = 9
Solving this equation takes one step, a division by 3. It works the other way too. An equilateral triangle with side 7 has perimeter 3 × 7 = 21. Every side is the same, so knowing the perimeter tells you the whole triangle.
Challenge
An equilateral triangle has perimeter 42.
Find its side s.
Try it yourself
Solve for s
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