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...

Use your pupils' sense of curiosity to explore the Parallelogram Law. Here is an activity that outlines a complete lesson plan from beginning to end, allowing pupils to follow a conjecture through to the proof stage.

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....

Students identify different properties of parallelograms. In this geometry lesson, students complete problems that proves the theorems and properties of parallelograms. They graph the different shapes on paper.

Students apply definitions and theorems to verify special quadrilaterals using coordinate geometry. They apply the slope formula, the midpoint formula, and the distance formula to justify that a given quadrilateral is a parallelogram....

Rhombuses, rectangles and squares are have special properties. In this lesson, young geometers investigate and make conjectures about diagonals, angles, and parallel lines of parallelograms. 

Do you view proofs as an essential geometric skill? The resource builds on an understanding of dilations by proving the Dilation Theorem of Segments. Pupils learn to question and verify rather than make assumptions. 

So many times the characteristics of triangles are presented as a vocabulary-type of lesson, but in this activity they are key to unraveling a proof. A unique attack on proving that an inscribed angle that subtends a diameter must be a...

What type of quadrilateral is that? Discover the difference between the types of quadrilaterals. Small groups investigate types of quadrilaterals using geometry software to find their properties. To keep track of the different...

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...

Students broaden their outlook on geometry in their everyday environment. They explore the properties of parallel lines and parallelograms and discover ways to prove the existence of parallel lines and discuss the concept of parallel lines.

Students prove conjectures about geometric figures on the plane or in space using coordinate geometry. They develop fluency in operations with real numbers, vectors and matrices using mental computation or paper-and-pencil calculations...

Tenth graders connect the history of geometry to problem solving. In this geometry lesson, 10th graders investigate polygons through hands on manipulatives and solve problems relating to parallelograms and triangles. They calculate the...

Students explore the concept of quadrilaterals. In this quadrilaterals lesson, students use the slope formula, midpoint formula, and distance formula to justify that a given quadrilateral is a parallelogram.

Challenge your class to construct a definition for trapezoids. Looking at four examples and four non-examples, students individually create definitions and use them to classify an unknown shape. Allow for small group and whole-class...

Medians, midsegments, altitudes, oh my! Pupils study the properties of the median of a triangle, initially examining a proof utilizing midsegments to determine the length ratio of a median. They then use the information to find missing...

Ninth graders identify quadrilaterals and label the vertices of quadrilaterals. they justify their identification of the quadrilaterals. Students work in groups to identify and create quadrilaterals

Ninth graders investigate quadrilaterals.  In this geometry lesson, 9th graders examine and classify quadrilaterals using the slope, midpoint and distance formulas.  Additionally, students create various quadrilaterals given...

In this task, a student has learned the SSS and SAS congruence tests for triangles and wonders if these tests might work for parallelograms. Aligns with G-CO.C.11 and G-SRT.B.5

In the pictured quadrilateral, opposite sides are congruent and learners must explain whether this makes it a parallelogram. Aligns with G-CO.C.11.

Suppose that ABCD is a parallelogram and that M and N are the midpoints of lines AB and CD respectively. Students are asked to prove that MN=AD, and that the line MN is parallel to line AD. Aligns with G-CO.C.11.

In this task, students are asked to draw a quadrilateral so that no two sides are congruent, no two angles are congruent, and no two sides are parallel. The task gives students the opportunity to prove that if we join the midpoints of a...