2. • Angles are in different shapes
and sizes. Some are wide and
some are narrow angles. All
angles can be measured as
part of a circle. It can be in
degree radius. Use a protractor
in measuring angles. Angles
are measured in degrees.
ANGLES
3. Angles are named by writing the names of three
points on the set of lines.
• Angle BXM or BXM
∠
• Angle MXB or MXB
∠
You can also name an angle by its vertex as:
• ∠X ; angle X
5. How is an angle measured by a protractor?
• Place the middle point of the protractor
on the vertex of the angle.
• Read the number of the degrees shown
by the other ray. ∠DSE = 35°
Other examples.
6. D. Angle
An angle is the union of two rays that meet at a
common point called vertex.
An angle is measured using a measuring device
called protractor. The unit used to measure
angle is called degree.
A
B C
7. E. KINDS OF ANGLE
The kind of angle is determined by the
amount of its opening.
An acute angle is an angle whose measure
is less than 90°
An obtuse angle is an angle whose measure is
greater than 90° but less than 180°
A right angle is an angle whose measure is 90°.
A straight angle is an angle whose
measure is 180°
A reflex angle is an angle that measures between 180° and 3
8. Below are the illustrative examples of the different
angles.
9. 1. Complementary Angles
These are two angles whose sum of measure is 90°.
∠ABD and DBC are complementary angles.
∠
10. 2. Supplementary Angles
These are two angles whose sum of measure is 180°
∠LMO and OMN are supplementary angles.
∠
11. Symmetry
A figure has line symmetry if it can be folded in half
so its two parts match exactly.
Look at the figure formed. It is exactly two
halves.
The line along the fold dividing the figure is a line
12. A figure can have more than one line of symmetry
