What is the name of the figure that has three sides and three angles?
Recognise right angles, angles on a straight line and angles at a point Identify the vertex and arms of angles formed by intersecting lines Identify angle types formed by the intersection
An angle is the space between two lines or the corner of a shape. Angles are measured in degrees. Common angles are right angles (90°), acute angles (less than 90°) and obtuse angles (more than 90°). Angles are used in everyday life to measure distances and build shapes.
What are Angles?
Angle: A figure formed by two lines or rays that start at the same point and go in different directions. Acute Angle: An angle that measures less than 90 degrees but more than 0 degrees. Obtuse Angle: An angle that measures more than 90 degrees but less than 180 degrees. Right Angle: An angle that measures exactly 90 degrees. Reflex angle: An angle that measures more than 180 degrees but less than 360 degrees. Revolution: An angle that measures exactly 360 degrees.
Angles can be measured in degrees. The angle of a straight line is 180 degrees. The angles of a triangle always add up to 180 degrees.
Did you know?
Work together in pairs: What is the name of the angle formed when two lines intersect at the same point?
An angle formed when two lines intersect at the same point is called a "vertex angle". Let's discuss why..
Question: What are some real life examples of right angles, angles on a straight line and at a point? Clues: • Look around the school and find examples of objects that have right angles. • Think about objects that have a straight line and how that line could create an angle or several angles. • Look at the corner of a table, chair, or other object and see if the corner creates an angle. • Right angles can be found in buildings, furniture, and even toys. Angles on a straight line can be seen in roads, lines, and paths. • Angles at a point can be seen in the corners of walls, in the petals of a flower, or in the tire of a car. In pairs: Select and solve one of the tasks: A. Draw a picture of a real life example of a right angle, angle on a straight line and at a point. B. Share your drawing with the class and explain why each object meets the criteria.
Brain break: Draw a monkey carrying a banana umbrella and wearing swimming goggles
Angles on a straight line
Angles on a straight line relate to the sum of angles that can be arranged together so that they form a straight line. Angles on a straight line add to 180°.
Right angles on a line
We know that a right angle is equal to 90 degrees. This can help us find the measurement for other angles on a straight line by subtracting 90 degrees from 180 to find what the sum of the remaining angles will be.
Open questions activity
What do you notice about the angles in this image? Can you identify the vertex and arms of the angles that intersect?
Properties of an angle
You would have noticed that the intersecting angles can share the same arms and vertex.
When two lines intersect, like the blades of a pair of scissors, a number of angle pairs are formed. You can find relationships between the measures of the angles in each pair.
In your book
Using a straightedge, draw a pair of intersecting lines like the open scissors. Label the angles formed as 1, 2, 3, and 4. For example Use a protractor to measure each angle. What do you notice?
Angles at a point: Revolution
What do you already know about an angle of revolution? How can this knowledge help you identify the size of each of these angles?
Work with a partner: Can you identify the vertex and arms of angles formed by intersecting lines in this image?
Draw three angles that intersect and identify the vertex and the arms of the angles.