# Ch 41: GACE Middle Grades Math: Triangle Theorems & Proofs

### About This Chapter

## GACE Middle Grades Math: Triangle Theorems & Proofs - Chapter Summary

Our instructors re-familiarize you with various triangle theorems and proofs to get you ready to answer geometry questions on the GACE Middle Grades Mathematics test. Lessons cover the following topics:

- Applications of similar triangles
- The SAS, ASA and SSS triangle congruence postulates
- The converse of a statement
- Similarity transformations in corresponding figures
- Using congruence and similarity to prove relationships in figures
- The AAS, HA and HL theorems
- The perpendicular bisector and angle bisector theorems
- The LA and LL theorems
- Congruency of isosceles triangles

These short, engaging video lessons offer an easy way to study geometry. Re-watch the video lessons as often as necessary to grasp the materials, or, if you want to see only main points, use video tags to jump to that section of the lesson. Video lessons often include links to text lessons that detail key terms. Lesson transcripts also can be used as an additional study aid.

### 1. Applications of Similar Triangles

Similar triangles are used to solve problems in everyday situations. Learn how to solve with similar triangles here, and then test your understanding with a quiz.

### 2. Triangle Congruence Postulates: SAS, ASA & SSS

When we have two triangles, how can we tell if they're congruent? They may look the same, but you can be certain by using one of several triangle congruence postulates, such as SSS, SAS or ASA.

### 3. Congruence Proofs: Corresponding Parts of Congruent Triangles

Congruent triangles have congruent sides and angles, and the sides and angles of one triangle correspond to their twins in the other. In this lesson, we'll try practice with some geometric proofs based around this theorem.

### 4. Converse of a Statement: Explanation and Example

Just because a conditional statement is true, is the converse of the statement always going to be true? In this lesson, we'll learn the truth about the converse of statements.

### 5. Similarity Transformations in Corresponding Figures

Watch this video lesson to learn how you can tell if two figures are similar by using similarity transformations. Learn how to find the corresponding sides and angles and then how to compare them.

### 6. How to Prove Relationships in Figures using Congruence & Similarity

In this lesson, we'll look at similar and congruent figures and the properties that they hold. We will then look at how to use these properties to prove relationships in these figures in various examples.

### 7. Practice Proving Relationships using Congruence & Similarity

In geometry, if two shapes are similar they have the same shape but different sizes, while two congruent shapes have the same shape and size. In this lesson, you will learn how to prove that shapes are similar or congruent.

### 8. The AAS (Angle-Angle-Side) Theorem: Proof and Examples

When trying to find out if triangles are congruent, it's helpful to have as many tools as possible. In this lesson, we'll add to our congruence toolbox by learning about the AAS theorem, or angle-angle-side.

### 9. The HA (Hypotenuse Angle) Theorem: Proof, Explanation, & Examples

In this lesson, we'll learn about the hypotenuse angle theorem. With this theorem, we can prove two right triangles are congruent with just congruent hypotenuses and acute angles.

### 10. The HL (Hypotenuse Leg) Theorem: Definition, Proof, & Examples

In this lesson, we'll learn about the hypotenuse leg theorem. This theorem enables us to prove two right triangles are congruent based on just two sides.

### 11. Perpendicular Bisector Theorem: Proof and Example

Perpendicular bisectors are multifunctional lines. They're not only perpendicular to the line in question, they also neatly divide it into two equal halves. In this lesson, we'll learn about the perpendicular bisector theorem.

### 12. Angle Bisector Theorem: Proof and Example

The angle bisector theorem sounds almost too good to be true. In this lesson, we set out to prove the theorem and then look at a few examples of how it's used.

### 13. Congruency of Right Triangles: Definition of LA and LL Theorems

In this lesson, we'll learn two theorems that help us prove when two right triangles are congruent to one another. The LA theorem, or leg-acute, and LL theorem, or leg-leg, are useful shortcuts for proving congruence.

### 14. Congruency of Isosceles Triangles: Proving the Theorem

Isosceles triangles have two equal sides. Are the base angles also equal? In this lesson, we'll prove how this is true. We'll also prove the theorem's converse.

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### Other Chapters

Other chapters within the GACE Middle Grades Mathematics (013): Practice & Study Guide course

- GACE Middle Grades Math: Basic Arithmetic Operations
- GACE Middle Grades Math: Solving Math Word Problems
- GACE Middle Grades Math: Properties of Numbers
- GACE Middle Grades Math: Roots & Radical Expressions
- GACE Middle Grades Math: Exponents & Exponential Expressions
- GACE Middle Grades Math: Scientific Notation
- GACE Middle Grades Math: Simplifying Expressions
- GACE Middle Grades Math: Integers
- GACE Middle Grades Math: Rational Numbers
- GACE Middle Grades Math: Introduction to Fractions
- GACE Middle Grades Math: Operations with Fractions
- GACE Middle Grades Math: Introduction to Decimals
- GACE Middle Grades Math: Operations with Decimals
- GACE Middle Grades Math: Percents
- GACE Middle Grades Math: Rates, Ratios & Proportions
- GACE Middle Grades Math: Number Theory
- GACE Middle Grades Math: Factoring
- GACE Middle Grades Math: Estimating & Rounding
- GACE Middle Grades Math: Monomials & Polynomials
- GACE Middle Grades Math: Writing Algebraic Expressions
- GACE Middle Grades Math: Basic Algebraic Expressions
- GACE Middle Grades Math: Algebraic Distribution
- GACE Middle Grades Math: One-Step Equations
- GACE Middle Grades Math: Two-Step Equations
- GACE Middle Grades Math: Rational Expressions
- GACE Middle Grades Math: The Coordinate Graph
- GACE Middle Grades Math: Linear Equations
- GACE Middle Grades Math: Systems of Linear Equations
- GACE Middle Grades Math: Negative Numbers
- GACE Middle Grades Math: Absolute Value
- GACE Middle Grades Math: Inequalities
- GACE Middle Grades Math: Number Patterns & Sequences
- GACE Middle Grades Math: Properties of Functions
- GACE Middle Grades Math: Graphing Functions
- GACE Middle Grades Math: Perimeter & Area
- GACE Middle Grades Math: Polyhedrons & Geometric Solids
- GACE Middle Grades Math: Symmetry, Similarity & Congruence
- GACE Middle Grades Math: Properties of Lines
- GACE Middle Grades Math: Angles
- GACE Middle Grades Math: Triangles
- GACE Middle Grades Math: Similar Polygons
- GACE Middle Grades Math: The Pythagorean Theorem
- GACE Middle Grades Math: Quadrilaterals
- GACE Middle Grades Math: Circles
- GACE Middle Grades Math: Circular Arcs & Measurement
- GACE Middle Grades Math: Transformations
- GACE Middle Grades Math: Measurement
- GACE Middle Grades Math: Data & Graphs
- GACE Middle Grades Math: Sets
- GACE Middle Grades Math: Statistics
- GACE Middle Grades Math: Data Collection
- GACE Middle Grades Math: Samples & Populations
- GACE Middle Grades Math: Probability
- GACE Middle Grades Mathematics Flashcards