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Sorting by Sides

Part of the Triangles section of Coddy's Geometry journey. Lesson 5 of 60.

Triangles have names by their sides:

Equilateral: all three sides are equal.
Isosceles: at least two sides are equal.
Scalene: no two sides are equal.

We write a triangle with corners A, B and C as △ABC. Equal sides have the same tick marks. A tick mark is a small line across a side. The same number of ticks means the same length. Trust the marks, not the drawing. The two equal sides can point in any direction.

$Triangle PQR with sides QR and RP each carrying two tick marks$

Challenge

Drag C until △ABC is isosceles, with AC as long as AB. Watch the three lengths as you drag. Then press Check.

Try it yourself

$Drag the figure and watch$

Drag the figure and watch

All lessons in Triangles

1The Triangle Inequality

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

4Area of a Triangle

Half the Rectangle Height Is Not a Side Right Triangle Area Finding the Height Any Side Can Be the Base Recap: Area

7Is It Right?

The Converse Testing a Triangle Acute or Obtuse?Sorting by the Test Recap: Right or Not

10Scale in the World

Shadows Across the River Nested Triangles A Side with an Expression Recap: Scale in the World

2Sides and Names

Sorting by SidesThe Longest Side Ticks into Equations Recap: Sorting Triangles

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