1. Perpendicular Definition: Lines that meet at a 90 degree angle.
Symbol: ⊥
For example: 𝐴𝐵 ⊥ 𝐶𝐷
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2. Parallel Definition: Lines that never intersect (cross/touch).
Symbol: ∥
Example: 𝑆𝑇 ∥ 𝐶𝐺
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3. Defining Geometry Terms…
Definition- a statement that clarifies or explains the meaning of a word or phrase.
Counterexample- Something that follows the definition, but is not the intended response.
Car- Has four wheels, steering wheel and moves people from one place to another.
What is a counterexample to this definition?

4. Steps to a Good Definition
Classify your term. What is it?
Differentiate your term. How does it differ from other in that class?
Test your definition by looking for a counterexample.

5. Example for a Square Classify your term. What is it?
Four sided figure
Differentiate your term. How does it differ from other in that class?
with four congruent sides and four right angles.
Test your definition by looking for a counterexample.
Definition: Four sided figure with four congruent sides and four right angles.

6. Complementary Angles Definition: 2 angles that add up to 90 degrees.
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7. Supplementary Angles Definition: 2 angles that add up to 180 degrees.
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8. Linear Pair of Angles
Definition: Two angles on one line. Sum to 180 degrees.
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9. Right Angle Definition: Angle measure of exactly 90 degrees.
Symbol: Drawn with a “box”
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10. Acute Angle Definition: Angle measure of less than 90 degrees.
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11. Obtuse Angle
Definition: Angle measure of more than 90 degrees, but less than 180.
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