TOPIC 3 · GRADES 3–4 BRIDGE

Triangle Detectives

Classify triangles by side lengths and by the kinds of angles they contain.

Enrichment bridge to angle attributes

BIG IDEA

Every triangle has three straight sides and three angles, but triangles can belong to more than one category at once.

WHAT TO KNOW

By sides: equilateral has three equal sides, isosceles has at least two, and scalene has none equal.
By angles: acute has three acute angles, right has one right angle, and obtuse has one obtuse angle.
A triangle can have two names, such as right isosceles, because the names describe different attributes.

WATCH OUT

A triangle does not need to point upward. Turning or resizing it does not change its defining attributes.

TRY IT

Choose triangle families and compare the side marks and angle clues.

Choose the next topic from the lesson rail when you are ready.