Proofs Teacher Resources

Find Proofs lesson plans and worksheets
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Lesson Planet

Flippin' Proofs Parallel Lines Project

For Teachers 10th - 12th Standards
Learners will "flip" for this creative way to practice writing and explaining two-column proofs about parallel lines.  As they create their masterpiece, young geometers are led to consider overall proof characteristics as well as...
2:55
Lesson Planet

Parallel Lines and Transversals: Lesson

For Students 7th - 11th Standards
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...
3:42
Lesson Planet

Parallel Lines in the Coordinate Plane: Lesson

For Students 8th - 10th Standards
Discover the parallel structure of parallel lines. Provided with two parallel lines on a coordinate plane, the presenter shows that the rise and run, or slope, of the two lines are the same. The resource, which is a portion of a larger...
3:03
Lesson Planet

Parallel Lines 2

For Students 7th - 9th
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.
Lesson Planet

Proving Slope Criterion for Parallel Lines 1

For Students 9th - 12th Standards
Parallel lines and the slope formula...two seemingly distinct concepts, but a connection exists nonetheless. Young mathematicians prove that if two lines are parallel, then their slopes are equal. They have the option of using a...
EngageNY

Looking More Carefully at Parallel Lines

For Students 9th - 10th Standards
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...
1 In 1 Collection
EngageNY

Characteristics of Parallel Lines

For Teachers 8th Standards
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...
Lesson Planet

Parallel Lines, Transversals, and Angles: What’s the Connection?

For Students 9th - 11th Standards
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...
3:57
Lesson Planet

Distance Between Parallel Lines: Lesson

For Students 9th - 12th Standards
Rely on slope when counting won't do. Using horizontal and vertical parallel lines, the presentation shows scholars how to find the distance by counting. The video uses the relationship of the slopes of perpendicular lines to find two...
Lesson Planet

Parallel Lines Cut by a Transversal

For Teachers 9th - 12th Standards
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...
Lesson Planet

Parallel Lines

For Students 10th
In this parallel lines activity, 10th graders solve and complete 55 various types of problems. First, they prove that the lines shown are parallel. Then, students complete each two-column proof for the parallel lines shown. They also...
Lesson Planet

Proving Slope Criterion for Parallel Lines 2

For Students 9th - 12th Standards
There's a simple way to tell if lines are parallel. Individuals prove that if lines a and b have the same slope, then they are parallel. Proofs will likely depend on similar triangles and alternate interior angles.
Lesson Planet

Conjectures and Proof

For Students 9th - 12th Standards
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...
Lesson Planet

Parallel Lines Cut By a Transversal

For Teachers 9th - 12th Standards
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,...
1 In 1 Collection
EngageNY

Informal Proofs of Properties of Dilations

For Teachers 8th Standards
Challenge the class to prove that the dilation properties always hold. The lesson develops an informal proof of the properties of dilations through a discussion. Two of the proofs are verified with each class member performing the...
Lesson Planet

Accurately Acquired Angles

For Teachers 9th - 12th Standards
From any angle, the resource on proving angle relationships is a good one to use. Scholars first engage in activities that enable them to identify types of angles when a transversal cuts two parallel lines. In groups, they prove a...
EngageNY

Unknown Angle Proofs—Proofs of Known Facts

For Teachers 9th - 10th Standards
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...
1:57
Lesson Planet

Alternate Interior Angles: Lesson

For Students 9th - 12th Standards
Concepts of alternate interior angles parallel the concepts of corresponding angles. Using a diagram, the presentation defines and identifies alternate interior angles formed by a transversal and two parallel lines. The video in a...
Lesson Planet

Accelerated Geometry Review Sheet

For Students 8th - 10th Standards
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;...
Lesson Planet

Parallel Lines Proofs Practice

For Students 8th - 11th Standards
Here is a worksheet that lines up perfectly with the skills needed to finish a geometric proof. Eleven problems are given to see if learners can prove that lines are parallel or angles are congruent. 
EngageNY

Triangle Congruency Proofs (part 1)

For Teachers 9th - 10th Standards
Can they put it all together? Ninth graders apply what they know about proofs and triangle congruence to complete these proofs. These proofs go beyond the basic triangle congruence proofs and use various properties, theorems, and...
1 In 1 Collection
EngageNY

Congruence, Proof, and Constructions

For Teachers 8th - 10th Standards
This amazingly extensive unit covers a wealth of geometric ground, ranging from constructions to angle properties, triangle theorems, rigid transformations, and fundamentals of formal proofs.  Each of the almost-forty lessons is broken...
Lesson Planet

Semester 1 Review for Geometry final

For Students 10th
In this geometry activity, 10th graders solve problems that are based on the topics covered in a first semester geometry class, including, linear equations and the equations of parallel and perpendicular lines, the logic of geometry,...
Lesson Planet

Joining Two Midpoints of Sides of a Triangle

For Teachers 9th - 11th Standards
Without ever using the actual term, this exercise has the learner develop the key properties of the midsegment of a triangle. This task leads the class to discover a proof of similar triangles using the properties of parallel lines cut...

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