Mathematics 7: Angles (naming, types and how to measure them)
- 5. E O N P A G M L B S
- 7. An angle is defined as the amount of turn between two straight lines that share a common end point. Angles are measured in degrees. The symbol used for degrees is a little circle °.
- 8. VERTEX The vertex of an angle is the common point where the two lines meet. ARM The arms of an angle or sides are the lines that make up the angle. DEGREES The size of the angle is measured in degrees and usually denoted with the ° symbol. For example, an angle may measure 45°. PROTRACTOR A tool that is used to measure angles.
- 10. There are different ways to name angles. One way is to use the ∠ symbol followed by three letters. From the diagram below you see ∠BAC. The first and third letters indicate points on the two arms. The letter in the middle is the vertex. The first and third letters can be switched because they measure the same angle. For example, ∠BAC is the same as ∠CAB.
- 11. ACUTE RIGHT OBTUSE STRAIGHT
- 12. An acute angle is an angle that measures greater than 0° and less than 90°.
- 13. A right angle is an angle that measures 90°.
- 14. An obtuse angle is an angle that measures greater than 90° and less than 180°.
- 15. A straight angle looks like a straight line and measures 180°. It is half a revolution of a circle.
- 18. A Protractor has two scales: •The outer scale reads from 0° to 180° reading from left to right. •The inner scale reads from 0° to 180° reading from right to left.
- 19. To measure ∠ABC: 1.Place the center of the protractor on the vertex B. 2.Adjust the 0° line or baseline of the protractor so that it lines up with line BC. 3.Since the angle is acute and the 0° line or baseline was used from the right, you will take the reading from the inner scale.
- 20. If an angle is facing the other direction and the 0° line or baseline was used on the left, the outer scale will be used. Since it is on the left and you know the angle is obtuse, reading from left to right the measurement is 100°.
- 26. Identify the following angles based on their figure/measures.