EngageNY
Review of the Assumptions (part 2)
Is the amount of information getting overwhelming for your geometry classes? Use this strategy as a way to organize information. The resource provides a handout of information studied in relation to triangle congruence. It includes a...
Curated OER
Geometry, Measurement & Reasoning
Students construct two-column proofs. In this geometry activity, students use deductive reasoning and geometric properties to justify given geometric statements. Students compare and contrast proofs.
Curated OER
Paragraph Proofs
Students explore the concept of paragraph proofs. In this paragraph proofs lesson, students make flow charts of the process of getting ready for school. Students convert the flow chart to a paragraph proof. Students use geometric...
Curated OER
The Truth About Triangles And Proofs
Students engage in a lesson plan that is about the classification of triangles and the mathematical proofs involved in working with them. They work on a variety of problems that are created by the teacher with the focus upon the...
EngageNY
Solve for Unknown Angles—Angles and Lines at a Point
How do you solve for an unknown angle? For this sixth installment of a 36-part series, young mathematicians use concepts learned in middle school geometry to set up and solve linear equations to find angle measures.
EngageNY
Proving the Area of a Disk
Using a similar process from the first lesson in the series of finding area approximations, a measurement resource develops the proof of the area of a circle. The problem set contains a derivation of the proof of the circumference formula.
EngageNY
Properties of Parallelograms
Everyone knows that opposite sides of a parallelogram are congruent, but can you prove it? Challenge pupils to use triangle congruence to prove properties of quadrilaterals. Learners complete formal two-column proofs before moving on to...
EngageNY
Ptolemy's Theorem
Everyone's heard of Pythagoras, but who's Ptolemy? Learners test Ptolemy's Theorem using a specific cyclic quadrilateral and a ruler in the 22nd installment of a 23-part module. They then work through a proof of the theorem.
Curated OER
Triangle's Interior Angles
Given a pair of parallel lines and a triangle in between, geometers prove that the sum of the interior angles is 180 degrees. This quick quest can be used as a pop quiz or exit ticket for your geometry class.
Curated OER
Two Column Logic Proofs
Pupils complete two column proofs. In this geometry instructional activity,students derive the reasons their answers are correct using logic. They write the proof step by step using two columns.
Curated OER
Indirect Proof and Inequalities in One Triangle
In this geometry worksheet, 10th graders order the sides and angles of a triangle and determine the range of the third side of a triangle given the lengths of two sides. The one page worksheet contains sixteen questions. Answers are...
Curated OER
Coordinate Proofs
Students explore the concept of coordinate proofs. In this coordinate proofs lesson plan, students write coordinate proofs using properties of distance, slope, and midpoint. Students discuss why it is sometimes beneficial to double the...
EngageNY
Unknown Angle Proofs—Proofs of Known Facts
Lead the class in a Greek history activity 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...
EngageNY
Analytic Proofs of Theorems Previously Proved by Synthetic Means
Prove theorems through an analysis. Learners find the midpoint of each side of a triangle, draw the medians, and find the centroid. They then examine the location of the centroid on each median discovering there is a 1:2 relationship....
EngageNY
Mid-Module Assessment Task - Geometry (Module 1)
How do you prepare class members for the analytical thinking they will need in the real world? An assessment requires the higher order thinking they need to be successful. The module focuses on the concept of rigid transformations...
Illustrative Mathematics
Equal Area Triangles on the Same Base II
A deceptively simple question setup leads to a number of attack methods and a surprisingly sophisticated solution set in this open-ended problem. Young geometers of different strengths can go about defining the solutions graphically,...
Curated OER
Preparation and Transition to Two-Column Proofs
Students investigate proofs used to solve geometric problems. In this geometry lesson, students read about the history behind early geometry and learn how to write proofs correctly using two columns. The define terminology valuable to...
Curated OER
Probability and Geometry
Students practice calculating probability, see how geometry can help solve probability problems and explore platonic solids.
Curated OER
Pythagorean Theorem Proof
Tenth graders investigate the Pythagorean Theorem. Then they type up a formal paragraph proof of a proof of their choice.
Illustrative Mathematics
Joining Two Midpoints of Sides of a Triangle
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...
Curated OER
History / Introduction of Pythagorean Theorem
Learners explore Pythagoras and the history behind his theorem. They work together to solve a proof that is embedded in the instructional activity.
Curated OER
Proving Quadrilateral Properties
Working backwards can sometimes help you see a path to solving a problem. In this chapter, properites of quadrilaterials are proven by looking at flowcharts and working the probem backwards. Worked through examples are given, along with...
EngageNY
The Inscribed Angle Alternate – A Tangent Angle
You know the Inscribed Angle Theorem and you know about tangent lines; now let's consider them together! Learners first explore angle measures when one of the rays of the angle is a tangent to a circle. They then apply their newfound...
Illustrative Mathematics
Why Does SSS Work?
While it may seem incredibly obvious to the geometry student that congruent sides make congruent triangles, the proving of this by definition actually takes a bit of work. This exercise steps the class through this kind of proof by...
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