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Math Worksheets For All Ages

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# Geometric Proofs Worksheets

What are Geometric Proofs? We all have heard about proof. Generally speaking, proof is something that you need to establish a fact or determine something as true. But how do we prove something in geometry? How do we prove that the two angles are congruent or not? This is where geometric proofs play their role. So, let's begin with defining geometric proofs and discussing their types later on. GEOMETRIC PROOFS - A geometric proof is an approach of determining whether the statement is false or true by making use of logic, reasoning, facts and deductions to conclude an argument. A well-developed proof has its every statement supported by: Theorems: statements that can be proven true by using reasoning or support of previously established facts Postulates: statements that are assumed as truths without the need of proofs Axioms: statements that are considered as established and self-evident truths TYPES OF GEOMETRIC PROOFS - Geometric proofs are classified into: Direct Proof - In direct proofs, conclusions are derived from facts by using theorems and axioms and without making further assumptions. Indirect Proof - In indirect proofs, the statement to be proven is assumed as false. If the assumption results in an impossibility, then the supposed statement has to be proven true. Paragraph Proof - Paragraph proofs are logical arguments written in the form of a paragraph, supporting every step with evidences and details to provide a definite conclusion. Two-column Proof - Two-column proof comprises two columns with statements listed in one column while the reasons and logics for each statement stated in the second column. Their content is similar to paragraph proof but their form is different.

### Aligned Standard: High School Geometry - HSG-CO.C.9

• Answer Keys - These are for all the unlocked materials above.

### Homework Sheets

The first one focuses on angles, the second on lines and angles. The third one puts it all together.

• Homework 1 - We can see that ∠ABD and ∠CBD form a linear pair, so they are supplementary to each other.
• Homework 2 - Vertical angles are equal is the lead here.
• Homework 3 - Knowing that two lines are parallel, you can learn a lot.

### Practice Worksheets

We start to really concentrate on numerical angles here for the first time.

• Practice 1 - Given line ABD, m ∠DBC = 43° What is the value of ∠ABC?
• Practice 2 - Find the value of x in each case.
• Practice 3 - Find the missing angles.

### Math Skill Quizzes

This is applied geometric at it's best! These problems have endless real world connections.

• Quiz 1 - The lines b and c are parallel. Find b.
• Quiz 2 - Use the concept of parallel to make decisions.
• Quiz 3 - Find the alternate interior angles.

### Simple Strategies for Solving Geometric Proofs When you first start working with these types of problems you can easily get overwhelmed. You will need to be observant and take in all the information that is given to you. Once you fully grasp all the aspects of the battle map or in this case the coordinate plane, you can proceed to make sense of it and explain it to others. Here are some simple steps you can get into the habit of to solve them quicker and more efficiently:

Make a Plan and Outline - The best thing to do is to start by creating a plan for yourself. We would encourage you to start by talking it out or writing a short outline of how you should proceed with the problem. Once you have a brief outline, go over the plan to make sure that you did not leave anything out. The dots should connect from one to another. It is then helpful to plug numbers into those values to make sure that you are on the right path. Things that can help you along the way is to spot reference angles and sides of triangles. You can find most of this information by referring to the information that is given to you.

Spot What’s Not Stated - Look for congruent triangles because they can help you prove two sides and/or angles are the same through a number of different theorems. This will allow you to prove matching angles and spot balancing angles. Finding parallel lines is often golden. They will give you a flat surface to work off of. Look for triangles that are isosceles. Since they already have 2 equal sides you are just looking to see if the included angles are the same.

Practice If-Thens - We will begin to draft proofs based on what is given to us. To see if your assumptions make logical sense run the drafted proofs through if-then logic. Using these conditional statements, you should be able to understand if your proof makes sense. You need the conditional statement to be true.

Once you have all this in place, write your proof. Once complete, reverse engineer your proof to make sure that it works. Everything should flow equally in both directions as you progress through your proof. Following these simple steps often will be the key to your success.

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