# Ch 39: MTEL Mathematics (Elementary): Proof of Theorems

### About This Chapter

## MTEL Elementary Mathematics: Proof of Theorems - Chapter Summary

Proof of theorems is introduced in this chapter of the study guide. These lessons provide an introduction to the subject, including applications of similar triangles, triangle congruence postulates, and congruence proofs. The converse of a statement, and congruency are also covered by the lessons in this Proof of Theorems chapter. Other topics in this chapter include:

- Midpoint theorem
- Proof by contradiction
- Properties of right triangles
- Special right triangles
- The Pythagorean theorem
- The hypotenuse angle, hypotenuse leg, and angle-angle-side theorems

Knowledgeable instructors walk you through each subject using short, engaging video lessons, and are available to answer any questions you may have. Videos are accompanied by transcripts with important terms bolded, to help you study. The jump feature under the Timeline tab allows you to skip directly to main subjects within the videos, so you can review the subjects you need the most help with.

### 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. 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.

### 6. 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.

### 7. 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.

### 8. 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.

### 9. 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.

### 10. Midpoint Theorem: Definition & Application

Postulates and proven theorems allow us to know and understand certain things about geometric figures. In this lesson, we will be learning about the Midpoint Theorem.

### 11. Proof by Contradiction: Definition & Examples

One of several different ways to prove a statement in mathematics is proof by contradiction. Learn the definition of this method and observe how it is applied to proving a statement's truth value through examples and exploration.

### 12. Properties of Right Triangles: Theorems & Proofs

In this lesson, you will learn about the properties of and theorems associated with right triangles, which have a wide range of applications in math and science. Specifically, we will discuss and prove the Pythagorean theorem and the right triangle altitude theorem. Let's get started.

### 13. Special Right Triangles: Types and Properties

Not all right triangles are the same. In this lesson, we'll look at two special right triangles (30-60-90 and 45-45-90) that have unique properties to help you quickly and easily solve certain triangle problems.

### 14. The Pythagorean Theorem: Practice and Application

The Pythagorean theorem is one of the most famous geometric theorems. Written by the Greek mathematician Pythagoras, this theorem makes it possible to find a missing side length of a right triangle. Learn more about the famous theorem here and test your understanding with a quiz.

### 15. The Pythagorean Theorem: Converse and Special Cases

The Pythagorean Theorem is a famous theorem for right triangles. Watch this video to learn how the Pythagorean Theorem relates to the law of cosines and how the converse of the Pythagorean Theorem can help you identify right triangles.

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### Other Chapters

Other chapters within the MTEL Mathematics (Elementary) (53): Practice & Study Guide course

- MTEL Mathematics (Elementary): Number Sense
- MTEL Mathematics (Elementary): Mathematical Operations
- MTEL Mathematics (Elementary): Factoring & Divisibility
- MTEL Mathematics (Elementary): Real Numbers
- MTEL Mathematics (Elementary): Prime Factorization
- MTEL Mathematics (Elementary): Rational Numbers
- MTEL Mathematics (Elementary): Properties of Numbers
- MTEL Mathematics (Elementary): Roots
- MTEL Mathematics (Elementary): Exponents
- MTEL Mathematics (Elementary): Exponential Expressions & Scientific Notation
- MTEL Mathematics (Elementary): Absolute Value
- MTEL Mathematics (Elementary): Integers
- MTEL Mathematics (Elementary): Estimating & Rounding
- MTEL Mathematics (Elementary): Principles of Fractions
- MTEL Mathematics (Elementary): Operations with Fractions
- MTEL Mathematics (Elementary): Introduction to Decimals
- MTEL Mathematics (Elementary): Operations with Decimals
- MTEL Mathematics (Elementary): Percents
- MTEL Mathematics (Elementary): Descriptive Statistics
- MTEL Mathematics (Elementary): Summarizing Data
- MTEL Mathematics (Elementary): Principles of Sampling
- MTEL Mathematics (Elementary): Regression & Correlation
- MTEL Mathematics (Elementary): Principles of Probability
- MTEL Mathematics (Elementary): Properties of Functions
- MTEL Mathematics (Elementary): Understanding Algebraic Expressions
- MTEL Mathematics (Elementary): Solving Algebraic Equations
- MTEL Mathematics (Elementary): Properties of Linear Relations
- MTEL Mathematics (Elementary): Graphing Linear Equations
- MTEL Mathematics (Elementary): Properties of Ratios & Proportions
- MTEL Mathematics (Elementary): Properties of Polynomial Functions
- MTEL Mathematics (Elementary): Properties of Quadratic Functions
- MTEL Mathematics (Elementary): Properties of Rational Functions
- MTEL Mathematics (Elementary): Properties of Exponential Functions
- MTEL Mathematics (Elementary): Principles of Measurement
- MTEL Mathematics (Elementary): Principles of Geometry
- MTEL Mathematics (Elementary): Understanding Lines in Geometry
- MTEL Mathematics (Elementary): Principles of Geometric Figures
- MTEL Mathematics (Elementary): Properties of Triangles
- MTEL Mathematics (Elementary): Quadrilaterals
- MTEL Mathematics (Elementary): Polygons
- MTEL Mathematics (Elementary): Circles & Circular Arcs
- MTEL Mathematics (Elementary): Principles of Geometric Solids
- MTEL Mathematics (Elementary): Parallel Lines & Symmetry
- MTEL Mathematics (Elementary): Transformations in Geometry
- MTEL Mathematics (Elementary): Understanding Coordinate Geometry
- MTEL Mathematics (Elementary School) Flashcards