Quadrilaterals (I): Rectangle & Square

1Summary 重點摘要

4 sides, 4 angles. Rectangle: opposite sides equal; square: all sides equal.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Step 1: Count sides and cornersTo study a shape, first count how many sides and how many corners it has. A rectangle, for example, has 4 sides and 4 corners, and the four sides close up into a closed shape, so a rectangle is one kind of quadrilateral. A quadrilateral simply means a shape with four sides; remember the name.
2. Step 2: Rectangle featuresA rectangle's opposite sides are equal: in a rectangle 6 cm long and 4 cm wide, the top and bottom sides are both 6 cm, and the left and right sides are both 4 cm. Equal opposite sides are the first feature of a rectangle.
3. Step 3: Four right anglesTest the four corners of a rectangle with a set square: each one is exactly 90 degrees. Four right angles plus equal opposite sides are the full features of a rectangle; both must hold for it to be one. Test all four corners, not just one.
4. Step 4: Square featuresAll four sides of a square are the same length. A die's face, for example, is a square; if one side is 3 cm, all four sides are 3 cm. Its four corners are right angles too. Equal sides plus four right angles are the features of a square.
5. Step 5: A square is a special rectangleA square has equal opposite sides and four right angles, so it meets all the conditions of a rectangle; it only adds one more requirement: all four sides equal. So a square is a special rectangle, but a rectangle is not always a square. Remember this relationship and sorting shapes will not go wrong.
6. Step 6: Find examplesLook for the shapes you have learnt in daily life: doors and book covers are rectangles; many stickers and floor tiles are squares. When finding them, count the sides and corners first, then name the shape. Observing and comparing often helps you remember the features better.

4Diagrams Diagrams

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• Quadrilateral: 4 sides, 4 corners.
• Rectangle: opposite sides equal + 4 right angles.
• Square: all 4 sides equal + 4 right angles.
• A square is a special rectangle.
• Use a set square to check right angles.