The Primary School Leaving Examination (PSLE) in Mathematics covers a range of topics, including various properties of angles that are fundamental to understanding geometry. Here are some key angle properties and concepts that students preparing for the PSLE should be familiar with:

**Types of Angles**

**Acute Angle**

An angle less than 90 degrees is referred to as an acute angle. It's often visualised as a narrow angle, like the opening of a partially closed door.

### Right Angle

An angle exactly equal to 90 degrees is termed a right angle. It's symbolised by a small square in the corner, and it represents a quarter turn.

### Obtuse Angle

An angle greater than 90 degrees but less than 180 degrees is termed an obtuse angle. It's larger than a right angle but smaller than a straight angle.

Tip: We can also use the corner of a ruler to check for right angles.

Angle B is a right-angle

Angle C is bigger than a right angle

Angle A is smaller than a right angle

## Measuring Angles

To measure an angle, we utilise a protractor, a common geometry tool.When measuring angles with a protractor, the convention is to start from the initial side of the angle and measure either clockwise or counterclockwise depending on the angle's direction.

## Properties of Angles

### The sum of angles on a straight line is 180°

When two lines intersect, they form opposite angles on each side. These angles, when combined, form a straight line, and thus their sum is 180 degrees.

### The sum of angles at a point is 360°

When multiple lines intersect at a single point, the angles formed around that point add up to 360 degrees. This property is fundamental in understanding the relationship between angles in geometric shapes.

### Vertically Opposite Angles

When two straight lines cross, they form two pairs of vertically opposite angles. Vertically opposite angles are equal to each other. This property is crucial in solving various geometric problems involving intersecting lines.

In a nutshell, understanding the concept of angles and their properties is essential for Primary 5 & 6 students. From PSLE angle questions grasping the notion of vertically opposite angles and adjacent angles, a solid foundation in angle concepts sets the stage for tackling more complex geometric problems in higher grades.

By comprehending how rays meet to form angles, recognising the significance of a common vertex, and appreciating the difference between acute and obtuse angles, students can confidently navigate through the world of geometry. So, let's encourage our young learners to explore angles with curiosity and enthusiasm, as angles are not just lines meeting at a common point but windows to understanding the intricacies of shapes and spaces.

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