2D Shapes

1Summary 重點摘要

Recognise circle, triangle, square, rectangle.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Step 1: Count sides and cornersThe most basic way to tell shapes apart is to count how many sides and corners they have; these numbers are like an identity card for each shape. Example: a triangle has 3 sides and 3 corners, and a square has 4 sides and 4 corners. Run a finger slowly along each side while counting, and nothing will be missed and no side counted twice. A common mistake is counting too fast and jumping over a side at a corner, which turns a four-sided shape into three sides, so always point and count slowly.
2. Step 2: CircleThe circle is a very special shape: it has no straight sides and no corners, and its whole boundary is one closed curved line. Example: a ten-dollar coin is a circle; running a finger around its edge feels smooth, and no sharp corner can be found, so a circle has 0 straight sides and 0 corners. Why does a circle roll? Because every part of its edge curves the same way, with no flat part to stop it. A common mistake is saying a circle has no side at all; in fact it has one curved side, which is simply not straight.
3. Step 3: SquareA square has two important features: all four sides are the same length, and all four corners are right angles. Example: every face of a die is a square; measure with a ruler and all 4 sides are equal, and look at its 4 corners, which are all square like the corner of a book. Both conditions must hold at once; if even one side is different, it is not a square. A common mistake is calling a shape a square because its sides look about equal, but only measuring with a ruler can confirm that the sides are truly all the same.
4. Step 4: RectangleA rectangle also has 4 sides and 4 right angles, but it only asks the opposite sides to be equal: top and bottom equal, left and right equal. Example: a door is a rectangle; its top and bottom sides are the same length, its left and right sides are the same length, and all 4 corners are right angles, yet the top is longer than the left side, so it is not a square. A common mistake is calling every four-sided shape a rectangle; we must also check that the corners are right angles and the opposite sides are equal, both at once.
5. Step 5: Square vs rectangleA square and a rectangle are relatives: both have 4 sides and 4 right angles, and the only difference lies in the side lengths. Example: all 4 sides of a square are equal, while a rectangle has two longer sides and two shorter sides. Measure the sides with a ruler and you can tell them apart. Remember it this way: a square is a special rectangle, one whose four sides are all equal. A common mistake is thinking the two shapes are entirely different kinds; in fact, when all 4 sides of a rectangle become equal, it turns into a square.
6. Step 6: Find shapes around youShapes hide all around us, and practising finding them one by one makes recognition faster and faster. Example: a clock face is a circle, a sandwich cut from corner to corner gives triangles, a book cover is a rectangle, and a floor tile is a square. While searching, name each shape and say its feature, such as 'this is a circle, it has no corners'. A common mistake is judging by a rough look only, for example taking a square with rounded corners for a circle; when hunting for shapes, still count the sides and corners to confirm.

4Diagrams Diagrams

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• Count sides and corners to name a shape.
• Circle: 0 straight sides, 0 corners.
• Triangle: 3 sides, 3 corners.
• Square: 4 equal sides.
• Rectangle: opposite sides equal, 4 right angles.