Triangles
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Introduction to Triangles
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Welcome class! Today we're diving into the world of triangles. Can anyone tell me how many sides a triangle has?
Three sides!
Exactly! A triangle is a closed figure with three sides, three angles, and three vertices. Now, does anyone know about congruent triangles?
Are those triangles that are the same size and shape?
Great answer! Congruent triangles have identical measurements for their sides and angles, which is essential for geometry. Letβs remember this with the acronym 'CC.' What does 'CC' stand for?
'Congruent Correspondence!'
Correct! Keep that in mind. Letβs move on to the criteria for determining if two triangles are congruent.
Congruence Criteria
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Now, let's discuss five congruence criteria. Who can name one?
I know one! It's SSS, Side-Side-Side.
Fantastic! If all three sides of one triangle are equal to all three sides of another triangle, they are congruent. What about SAS?
That's Side-Angle-Sideβwhen two sides and the included angle are equal.
Right! And how about ASA?
That's Angle-Side-Angle!
Excellent, and AAS is similar, just two angles and a non-included side. Lastly, we have RHS for right triangles. Can anyone summarize that?
It involves the right angle, hypotenuse, and one side!
Perfect! You all are really getting this. Remember these criteria as they will help build strong mathematical foundations.
Properties of Triangles
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Let's explore properties of triangles. Who remembers what happens to angles opposite equal sides?
They are equal!
That's right! Sides opposite equal angles are also equal. Can we apply that property in a triangle with sides of varying lengths?
Yes, a shorter side would have a smaller angle opposite to it.
Exactly! Now for a quick memory aid, who can summarize this point using a simple phrase?
'Equal sides, equal vibes!'
Haha! I love it. Definitely helps to remember.
Inequalities in a Triangle
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Now, letβs discuss inequalities in triangles. Who can explain the relationship between angles and sides?
The larger angle has the longer side opposite to it.
Correct! And can someone help me with another point regarding two sides?
The sum of any two sides must be greater than the third side.
Exactly! Remember this with the phrase, 'Two sides must always outweigh the one!' Great understanding, class.
Introduction & Overview
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Definition of a Triangle
Chapter 1 of 1
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Chapter Content
A triangle is a closed figure with three sides, three angles, and three vertices.
Detailed Explanation
A triangle is one of the simplest shapes in geometry. It has three sides that connect to form a closed shape. Each point where two sides meet is called a vertex. The amount of space enclosed within these three sides is known as the area of the triangle.
Examples & Analogies
Think of a slice of pizza or a triangular traffic sign. Both examples showcase the three sides and three angles that define a triangle, making them easily recognizable shapes in our daily environment.
Key Concepts
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Congruent Triangles: Triangles that are identical in size and shape. Their corresponding angles and sides are equal, leading to five main criteria for congruence:
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SSS (Side-Side-Side): All sides are equal.
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SAS (Side-Angle-Side): Two sides and the included angle are equal.
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ASA (Angle-Side-Angle): Two angles and the included side are equal.
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AAS (Angle-Angle-Side): Two angles and a non-included side are equal.
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RHS (Right angle-Hypotenuse-Side): The hypotenuse and one side of a right triangle are equal.
Examples & Applications
Example 1: Triangle ABC is congruent to triangle DEF if AB = DE, BC = EF, and AC = DF (SSS criterion).
Example 2: To prove triangle ACD β triangle ABD, if AB = AC and AD is the midpoint of BC, we can use the ASA criterion.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Three sides to see, three angles too, triangles come in all sizes, just like me and you!
Stories
Once upon a time in Triangle Town, there lived three friends named Sides, Angles, and Vertices, who loved playing congruence games together!
Memory Tools
To remember the congruence criteria: SSS, SAS, ASA, AAS, RHS, think of 'Some Students Always Answer Right Happily!'
Acronyms
For the triangle inequality, use 'SAS' for 'Sum of Any two Sides' to be greater than the third.
Flash Cards
Glossary
- Triangle
A closed geometric figure with three sides, three angles, and three vertices.
- Congruent Triangles
Triangles that have the same size and shape with equal corresponding sides and angles.
- SSS
Congruence criterion stating that if all three sides of one triangle are equal to the three sides of another triangle, the two triangles are congruent.
- SAS
Congruence criterion indicating two sides and the included angle are equal.
- ASA
Congruence criterion that asserts two angles and the included side are equal.
- AAS
Congruence rule stating that if two angles and a non-included side are equal, the triangles are congruent.
- RHS
Congruence criterion that applies to right triangles with equal hypotenuse and one side.
- Triangle Inequalities
Properties that determine the relationship between the sides and angles of a triangle.
Reference links
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