Around the Edge

Part of the Triangles section of Coddy's Geometry journey. Lesson 12 of 63.

The perimeter of a shape is the distance all the way around its edge. For a triangle, walk along all three sides and add them up. The letter P stands for it.

$Triangle DEF with sides 10, 5 and 8$

Here the sides are 10, 5 and 8, so P = 10 + 5 + 8, which is 23. Units stay the same: if the sides are in centimetres, so is the perimeter.

On this stage, tap inside the triangle to ask for its perimeter and pick the rule Perimeter. The board adds the sides once it knows all three.

Challenge

Find the perimeter of △ABC: tap inside it, pick the rule that gives it, then press Check.

Try it yourself

$Find the marked part of the figure$

Find the marked part of the figure

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Triangles

2The Triangle Inequality

Can Three Sticks Meet?Exactly Reaching The Range of the Third Side The Formula Recap: The Third Side

5The Pythagorean Theorem

Squares on the Sides Finding the Hypotenuse Pythagorean Triples When It Is Not Whole Recap: The Hypotenuse

8Special Right Triangles

The 45-45-90 Triangle Legs from the Hypotenuse The 30-60-90 Triangle All Three Sides Which Triangle Is It?Recap: Special Triangles

11Two Tools at Once

Height of an Isosceles Area from the Height The Equilateral Triangle Right Triangle Perimeter Recap: Two Tools

3Perimeter

Around the EdgeA Missing Side Isosceles Perimeter Sides as Expressions Recap: Around the Edge

6Finding a Leg

Working Backwards The Ladder Which Side Is c?A Leg That Is Not Whole Recap: Finding a Leg

9Similar Triangles

Same Shape, Different Size The Scale Factor Finding a Side Matching the Corners Recap: Similar Triangles

12Final Challenges

Final: Three Sticks Final: The Fence Final: The Ladder Final: The Shadow Final: Master of Triangles