Cogito
Grade 3 Math · Chapter 7 · Lesson 1
The Quadrilateral Family
A square is a rectangle, and both are quadrilaterals.
10 problems · about 13 minutes · 3.G.A.1
What this lesson teaches
The child classifies quadrilaterals and recognizes that categories can contain one another.
- A quadrilateral is any shape with 4 straight sides.
- Squares, rectangles, rhombuses, and trapezoids are all quadrilaterals.
- One shape can have several correct names.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Line Plots With Fractions: Stacks of 2, 3, 4 and 1. How many measurements in all?
Answer 10
Why 2 + 3 + 4 + 1 = 10.
Review — Measuring to Halves and Fourths: How many fourths make three quarters?
Answer 3
Why Three fourths is three of the small marks.
Review — Two-Step Graph Problems: Bars of 40, 15 and 5. How many more is the first than the other two together?
Answer 20
Why 40 − 20 = 20.
Warm Up
Straightforward practice. Get the method working first.
3 problemsHow many sides does every quadrilateral have?
Answer 4
Why All quadrilaterals have 4 sides.
Can one shape have more than one correct name?
Answer Yes. A square is also a rectangle.
Why A shape belongs to every category whose rules it meets.
How many sides does a quadrilateral have?
Answer 4
Why The word means four sides.
Build It Up
The same ideas with more to keep track of.
1 problemIs a square a rectangle?
Answer Yes. It has 4 square corners.
Why Check the corners.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsIs a rhombus a quadrilateral?
Answer Yes.
Why Count its sides.
Is It a Quadrilateral?: Is a trapezoid a quadrilateral?
Answer Yes. It has 4 sides.
Why Any 4-sided shape is a quadrilateral.
The Other Way: Is every rectangle a square?
Answer No. A rectangle can be long and thin.
Why Every square is a rectangle, but not the other way round.