Mathematics topic

2. • What is an angle?
• Naming
• Types
• How to measure an angle

3. • An angle is defined as the amount of turn between two
straight lines that share a common endpoint.
• Angles are measured in degrees.
• The symbol used for degrees is a little circle ֯

4. • Vertex– the vertex of an angle is the common point
where 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 45֯
• Protractor– A tool that is used to measure angles.

6. • 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

7. • ACUTE
• RIGHT
• OBTUSE
• STRAIGHT
• REFLEX

8. • An acute angle is an angle that measures greater than 0֯
and less than 90 ֯

9. • A right angle is an angle that measures 90 ֯

10. • An obtuse angle is an angle that measures greater than
90 ֯ and less than 180 ֯

11. • A straight angle looks like a straight line and measures
180 ֯ . It is half a revolution of a circle.

12. • A reflex angle is an angle which is more than 180 ֯ and
less than 360 ֯

13. • 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.

14. • To measure ABC:
1. Place the center of the protractor on the vertex B.
2. Adjust the 0 degree line or baseline of the protractor so
that it lines up with line BC.
3. Since the angle is acute and the 0 degree line or
baseline was used from the right, you will take the
reading from the inner scale.

15. • If an angle is facing the other direction and the 0 degree
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
degree.