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Learning Activity 2:
Determine the Measure of Angle
A. Learning Indicators
In this mathematics lesson, the learning indicators that you must achieve after studying
this module are to explain the types of angles (right, acute, obtuse, straight and reflex), and
determine the solution to the problem about the size of the angle.
B. Learning Activities
The Concept of Understanding Angle Size
An angle is formed when two rays of a line meet at one point. As Ananda learned that
a line has a beginning and no end point. Notice the straight line formed between the backstaff
tool and the sun. The two straight lines form a certain angle that will determine the height of
the sun. Mathematically, the relationship between line rays and vertices is illustrated as follows.
Figure 8. Relationship of line rays and vertices
An angle is an area formed by two rays whose vertices coincide. An angle also has
several parts that make up the angle. The corner parts are:
i. The leg of the angle, the ray of the line that forms an angle, namely PA
ii. The vertex, the point where the base of the ray intersects the vertex of the angle, namely P.
iii. The area of the corner, the area formed between the two legs of the angle, namely PB.
An angle is formed by two lines rays that intersect at exactly one point. Then the point
of intersection is called the vertex. An angle can be given the symbol , , etc., or a point that
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