Proofs Teacher Resources
Find Proofs lesson plans and worksheets
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Lesson Planet Curated
Geometry Unit 2: Reasoning and Proof
The four lessons in the Geometry Unit 2 module are all about reasoning and proof. In the first lesson pupils watch a video introducing conditional statements and their related statements. Learners find out how to identify the hypothesis...
Lesson Planet Curated
Geometry Unit 3: Parallel and Perpendicular Lines
The Geometry Unit 3: Parallel and Perpendicular Lines Unit Module contains seven lessons, each with a video, teacher reference, practice packets and solutions, and corrective assignments. In the first lesson, pupils learn eight...
Lesson Planet Curated
Mathematics Vision Project: Interactive Applets
Ready, set, go! The Mathematics Vision Project provides a collection of 10 Interactive Applets that follow the progression of learning—to practice, develop, and solidify understanding. The interactives use engaging materials that include...
Lesson Planet Curated
Flipped Math: Geometry
Imagine taking a complete geometry course remotely! Eleven units make up the My Geometry course. Each unit follows the Flipped-Mastery cycle of learning, divided into two semesters. Pupils watch and take notes on a video that details the...
Lesson Planet Curated
Geometry Unit 5: Quadrilaterals and Polygons
One's knowledge of angles should measure up to expectations. Scholars watch a video to learn about angles in polygons. They first see how to partition a polygon into triangles to find the sum of the interior angle measures. They then...
CK-12 Foundation
Parallel Lines and Transversals: Lesson
Segment transversals proportionally. Given a diagram with three parallel lines and two transversals, the narrator of a short video points out the parallel lines cut the transversals proportionally. The portion of a long playlist on...
Khan Academy
Parallel Lines 2
Can you tell, algebraically, if three lines are parallel? In this video, Sal demonstrates how to rewrite linear equations in slope-intercept form and compare the slope of each line.
Radford University
Parallel Lines Cut by a Transversal
Use the parallel lines to find your way. After first reviewing geometric constructions and the relationships between angles formed by parallel lines and a transversal, young mathematicians write proofs for theorems relating to parallel...
Khan Academy
Parallel Lines From Equation, Mathematics I, High School Math
Here is a fairly basic video that uses three equations, each written in slope-intercept form, to determine whether the lines are parallel. Sal graphs each equation on the same coordinate plane to show how their slopes compare. The video...
EngageNY
Looking More Carefully at Parallel Lines
Can you prove it? Making assumptions in geometry is commonplace. This resource requires mathematicians to prove the parallel line postulate through constructions. Learners construct parallel lines with a 180-degree rotation and then...
EngageNY
Characteristics of Parallel Lines
Systems of parallel lines have no solution. Pupils work examples to discover that lines with the same slope and different y-intercepts are parallel. The 27th segment of 33 uses this discovery to develop a proof, and the class determines...
Radford University
Parallel Lines, Transversals, and Angles: What’s the Connection?
Streets, bridges, and intersections, oh my! Parallel lines and transversals are a present in the world around us. Learners begin by discovering the relationship of the angles formed by parallel lines and a transversal. They then apply...
Radford University
Parallel Lines Cut By a Transversal
Perhaps planning a city isn't so difficult after all. Scholars first perform geometric constructions and investigate how parallel lines are useful in real-world situations. They then work on a city design project, drawing street maps,...
Flipped Math
More with Proofs
Proofs may be as easy as 1, 2, 3 ... maybe. Pupils participate in creating four example proofs. The presentation uses a list of geometric properties to develop the proofs by filling in both the statements and reasons. Scholars practice...
EngageNY
Informal Proofs of Properties of Dilations
Challenge the class to prove that the dilation properties always hold. The instructional activity develops an informal proof of the properties of dilations through a discussion. Two of the proofs are verified with each class member...
GeoGebra
Conjectures and Proof
Transform proofs using triangle rotations. By rotating a triangle around various points, class members develop proofs. Participants prove relationships of alternative interior angles formed by parallel lines and the sum of the interior...
Khan Academy
Proof: sin(a+b)=(cos a)(sin b)+(sin a)(cos b)
Sal proves the sum of angles formula for sine, sin (a+ b) = cos (a) sin (b) + sin (a) cos (b), through a clear but rather non-intuitive proof. The proof is interesting as it uses the SOH-CAH-TOA model and requires one to recall some...
EngageNY
Unknown Angle Proofs—Proofs of Known Facts
Lead the class in a Greek history lesson with a geometric twist. Pupils relate a short video about geometric properties to modern-day methods of solving for unknown angles. They discuss parallel line theorems and complete practice...
Curated OER
Determining Angle Measure with Parallel Lines
Students observe and solve examples of corresponding angle postulates, alternate interior angle theorems, and exterior and consecutive angles. They complete the Determining Angle Measure With Parallel Lines worksheet.
Khan Academy
Proof: cos(a+b)=(cos a)(cos b)-(sin a)(sin b)
Using a similar method that he used to prove the sum of angles formula for sine, Sal shows the proof of the cosine sum of angles formula, cos (a+ b) = cos (a) cos (b) - sin (a) sin (b). This proof also uses the SOH-CAH-TOA model and some...
Flipped Math
Proving Lines Parallel
Show it can all be proved. Scholars learn the converses of the properties of parallel lines. Using the converses, pupils determine which lines are parallel based on angle measurements and practice using a flow proof to show that two...
Geometry Accelerated
Accelerated Geometry Review Sheet
Your geometry learners use their knowledge of various geometric concepts to write proofs. Starting with givens containing parallel line segments with transversals and triangles and quadrilaterals, and the mid-point and distance formulas;...
Flipped Math
Parallel Lines and Triangles
Triangles bring sums to geometry. The lesson presents two theorems dealing with the angles of a triangle. Pupils learn about the Triangle Sum Theorem and the Exterior Angle Theorem, and then apply the theorems to create equations and...
Curated OER
Parallel Lines
In this parallel lines worksheet, 10th graders solve and complete 16 different types of problems. First, they name the lines that are parallel to those listed. Then, students find that values that make each set of line parallel. They...
