Cogito
Grade 4 Math · Chapter 7 · Lesson 5
Sorting Shapes by Their Angles
What a shape has decides what it is called.
10 problems · about 15 minutes · 4.G.A.2
What this lesson teaches
The child classifies two-dimensional figures by parallel sides, perpendicular sides, and angle type.
- Shapes are named by their properties.
- A triangle can have at most one right angle.
- Every square is a rectangle, but not the other way round.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Lines, Rays, and Segments: At how many degrees do perpendicular lines cross?
Answer 90
Why 90 degrees.
Review — Angles Add Together: A right angle split into 25 and one more part. How big is that part?
Answer 65
Why 65 degrees.
Warm Up
Straightforward practice. Get the method working first.
4 problemsHow many right angles can a triangle have?
Answer 1
Why Two right angles would use all 180 with nothing left.
What names a shape?
Answer What it has: sides, angles, parallel lines.
Why Properties name a shape, not its position.
How many right angles does a rectangle have?
Answer 4
Why Every corner.
How many pairs of parallel sides does a rectangle have?
Answer 2
Why Opposite sides.
Build It Up
The same ideas with more to keep track of.
2 problemsIs every rectangle also a square?
Answer No. Its sides need not be equal.
Why It only works one way round.
Does turning a shape change its name?
Answer No.
Why The properties stay the same.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Square: Is every square also a rectangle?
Answer Yes. It has 4 right angles.
Why A square meets every rule for a rectangle.
The Triangle: How many right angles can a triangle have?
Answer 1
Why Only one, because the three angles total 180.