📐 Geometry · Basics
Angle Relationships flashcards
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All 16 flashcards at a glance
Card 1
What does ∠ABC mean, and which letter is the vertex?
The angle with sides along rays BA and BC. The middle letter, B, is the vertex.
Card 2
What is the difference between ∠ABC and m∠ABC?
∠ABC is the angle itself (a figure). m∠ABC is its measure, a number of degrees, such as m∠ABC = 70°.
Card 3
Define complementary angles.
Two angles whose measures add to 90°. They do not have to be adjacent.
Card 4
Define supplementary angles.
Two angles whose measures add to 180°. They do not have to be adjacent.
Card 5
How can you remember which is 90° and which is 180°?
C for Corner (90°) and S for Straight (180°). Also, C comes before S, and 90 comes before 180.
Card 6
What are adjacent angles?
Two angles with a common vertex and a common side that do not overlap. Their sum can be any amount.
Card 7
What is a linear pair?
Two adjacent angles whose outer sides form a straight line. They add to 180°.
Card 8
Are vertical angles adjacent?
No. They are opposite each other and share only the vertex. Vertical angles are equal.
Card 9
What are the complement and the supplement of 71°?
Complement: 90° − 71° = 19°. Supplement: 180° − 71° = 109°.
Card 10
What do the angles around a point add up to?
360°, when they share the vertex and fill the whole turn with no gaps and no overlaps.
Card 11
What is an angle bisector? What does it do to an 84° angle?
A ray from the vertex that splits the angle into two equal angles. It splits 84° into two angles of 42°.
Card 12
Write expressions for the complement and the supplement of an angle of x°.
Complement: (90 − x)°. Supplement: (180 − x)°.
Card 13
Angles 5x° and (x + 18)° are complementary. Find x.
5x + (x + 18) = 90, so 6x + 18 = 90, 6x = 72 and x = 12. The angles are 60° and 30°.
Card 14
Why can’t you assume that two angles are equal because they look equal in a diagram?
Diagrams are not drawn to scale unless marked. Trust given measures, equal-angle marks, right-angle squares and straight lines.
Card 15
How are angles classified by size?
Acute: between 0° and 90°. Right: exactly 90°. Obtuse: between 90° and 180°. Straight: exactly 180°.
Card 16
Three angles measure 20°, 30° and 40°. Are they complementary angles?
No. They add to 90°, but “complementary” is defined for exactly two angles. You can say the three angles add to 90°, but not that they are complementary.