Measuring Angles - Part One

Recap from Previous Lesson

• Understanding of different angles:
  • Right Angle: Exactly 90 degrees
  • Acute Angle: Less than 90 degrees
  • Obtuse Angle: More than 90 degrees

Today's Focus

• Measuring the angle between two rays using a Protractor.

Understanding Angles

• How to Determine Angle Size:
  • Small angles are less open, larger angles are more open.
  • Straight angle across is 180 degrees.
  • The degree of openness of rays determines angle measurement.

Using a Protractor

• Steps to Measure an Angle:

  1. Place the vertex of the angle at the center of the protractor.
  2. Align one ray with the baseline of the protractor.
  3. Extend the other ray through the protractor's measurement arc.
  4. Read the degree marks where the second ray crosses.

• Reading Scales on a Protractor:

  • Black Scale: External scale, measures from the baseline.
  • Blue Scale: Internal scale, measures from the opposite side.

Naming Angles

• Angles are named with three points: the vertex (middle point) and points on each ray.
  • Example: Angle HIJ or JIH (vertex point 'I' must be in the middle).

Problem Examples

Example 1

• Angle HIJ
  • Name: HIJ or JIH
  • Classification: Obtuse (larger than 90 degrees)
  • Measurement: 105 degrees

Example 2

• Angle JKL
  • Name: JKL or LKJ
  • Classification: Obtuse
  • Measurement: 130 degrees

Example 3

• Angle PQR
  • Name: PQR or RQP
  • Classification: Acute (smaller than 90 degrees)
  • Measurement: 15 degrees

Example 4

• Angle XYZ
  • Name: XYZ or ZYX
  • Classification: Right Angle
  • Measurement: 90 degrees

Example 5

• Angle ABC
  • Name: ABC or CBA
  • Classification: Obtuse
  • Measurement: 160 degrees

Example 6

• Angle DEF
  • Name: DEF or FED
  • Classification: Obtuse
  • Measurement: 145 degrees

Key Takeaways

• Practice how to align a protractor and read measurements correctly.
• Understand the difference between acute, obtuse, and right angles to correctly interpret a protractor's scale.

Next Steps

• Practice measuring angles with various problems to gain proficiency in using a protractor.