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At a Glance - Angles

Not to be confused with angels, angles are the pointed corners of shapes. Angles can be named three different ways.

This angle could be named any of these ways:

  • ABC (counterclockwise)
  • CBA (clockwise)
  • B (just the vertex)

Angle ABC

Look Out: when naming an angle using three letters, the vertex must always be the middle letter!

Types of Angles

Acute AngleAn angle less that 90°.

Lame joke: this angle is so small and a-cute!
Angle DEF
Obtuse AngleAn angle greater than 90°, but less than 180°.Angle GHI
Right AngleAn angle that is exactly 90°.

This is commonly denoted with a small box in the corner.
Angle KLM
Straight AngleA 180° angle.

It's - you guessed it - a straight line.
ABC line
Supplementary AnglesAngles that add up to 180°.

Supplementary Angles RST/TSU are supplementary angles.
Complementary AnglesAngles that add up to 90°.

NOQ and QOP are complementary.
Vertical AnglesWhen two lines intersect, opposite angles are called "vertical angles".
Vertical angles are congruent.

angle 1 is equal and congruent to angle 3
angle 2 is equal and congruent to angle 4

Oh, btw, congruent angles are two or more angles that have the same measurement.

Example 1

Plane VWZ

Refer to the following diagram to answer questions 1-4

Plane GFI

Exercise 1

Name two sets of complementary angles.

Exercise 2

Name two sets of vertical angles.

Exercise 3

Name four obtuse angles.

Exercise 4

Name four right angles.

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