Angles, symmetry and 2-D shapes
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给老师： 面向 Angles, symmetry and 2-D shapes（Primary Maths，Grade 4）的即用型课程幻灯片, 复习笔记——用在你的课堂上，或将该知识点作为学生可实时游玩的互动课堂活动来运行。
课程笔记
Points, Lines, and Angles
- A point is an exact spot. We name it with a capital letter, like point A.
- A line is straight and goes on forever in both directions. We write it as line AB.
- A line segment is part of a line with two endpoints. It does not go on forever.
- A ray has one endpoint and goes on forever in one direction.
- An angle is formed when two rays meet at a point. The shared point is the vertex.
- The two rays are called the sides of the angle. We write an angle as ∠ABC, where B is the vertex.
Measuring Angles
- We measure angles in degrees using the symbol °.
- A full turn around a point is 360°.
- A right angle is exactly 90°. It looks like the corner of a square.
- An acute angle is less than 90°. It is smaller than a right angle.
- An obtuse angle is more than 90° but less than 180°. It is bigger than a right angle.
- A straight angle is exactly 180°. It forms a straight line.
Parallel and Perpendicular Lines
- Parallel lines are lines that never meet. They stay the same distance apart.
- We write parallel lines like AB ∥ CD.
- Perpendicular lines meet at a right angle (90°).
- We write perpendicular lines like AB ⊥ CD.
- You can find perpendicular lines at the corners of a rectangle.
Triangles
- A triangle is a 2-D shape with 3 sides and 3 angles.
- Triangles can be named by their sides: equilateral (all sides equal), isosceles (two sides equal), and scalene (no sides equal).
- Triangles can also be named by their angles: acute (all angles acute), right (one right angle), and obtuse (one obtuse angle).
- The angles inside any triangle add up to 180°.
- An equilateral triangle is also acute because all its angles are 60°.
Quadrilaterals
- A quadrilateral is a 2-D shape with 4 sides and 4 angles.
- The angles inside any quadrilateral add up to 360°.
- A square has 4 equal sides and 4 right angles.
- A rectangle has 2 pairs of equal sides and 4 right angles.
- A parallelogram has 2 pairs of parallel sides. Opposite sides are equal.
- A rhombus has 4 equal sides, but its angles are not necessarily right angles.
- A trapezoid has only 1 pair of parallel sides.
Symmetry
- A shape has symmetry if you can fold it in half so the two halves match exactly.
- The fold line is called the line of symmetry.
- A square has 4 lines of symmetry.
- A rectangle has 2 lines of symmetry.
- An equilateral triangle has 3 lines of symmetry.
- A circle has infinite lines of symmetry.
- To complete a symmetric figure, draw the mirror image on the other side of the line.
Coordinates and Translations
- We use coordinates to describe positions on a grid. They are written as (x, y).
- The first number is the x-coordinate (how far across).
- The second number is the y-coordinate (how far up).
- The point (0,0) is called the origin.
- A translation is a slide. The shape moves without turning or flipping.
- To translate a shape, move every point the same distance in the same direction.
- For example, moving a shape 3 squares right and 2 squares up is a translation.
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练习题
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1.What is the name of the point where two rays meet to form an angle?
Easy- Avertex
- Bside
- Cedge
- Dcorner
2.Which of the following is a straight angle?
Easy- A90°
- B180°
- C360°
- D45°
3.An acute angle is greater than 90°.
EasyTrue or false?
4.Which of the following angles is obtuse?
Easy- A35°
- B90°
- C120°
- D180°
5.What is the measure of angle BAC if angle BAD = 30° and angle DAC = 45°?
Medium- A75°
- B15°
- C60°
- D90°
6.Which of the following are types of angles? (Select all that apply)
Medium- Aacute
- Bobtuse
- Cparallel
- Dright
7.Match each angle type with its measure.
Medium- right angle
- acute angle
- straight angle
- 90°
- less than 90°
- 180°
8.Put these angles in order from smallest to largest: 90°, 45°, 180°, 120°.
Medium- 45°
- 90°
- 120°
- 180°
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