Around the Edge
Part of the Triangles section of Coddy's Geometry journey. Lesson 15 of 71.
The perimeter of a triangle is the distance around its edge. To find it, add the three sides together. A triangle with sides 5, 6 and 8 has this perimeter:
Sides 5, 6 and 8
P = 5 + 6 + 8
P = 19
The letter P stands for the perimeter. It has the same unit as the sides, so if the sides are in centimetres, the perimeter is 19 cm.
The perimeter is the total length around the triangle. Add all three side lengths, measured in the same unit. For sides of 5, 6 and 8 units, the perimeter is 5 + 6 + 8 = 19 units.
Challenge
A triangle has sides 7, 9 and 12.
Find its perimeter P.
Try it yourself
Solve for P
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