Illustrative Mathematics
Find the Angle
This a fun problem for young geometers to play with while gaining important insight into deductive reasoning. Some will find the answers very quickly, others might take a less direct path, but all will use their knowledge of the sum of...
Curated OER
Altitude, Median, and Angle Bisector of a Triangle
Learners investigate the special properties of an altitude, a median, and an angle bisector and explore how these special segments divide the area of a triangle. The dynamic nature of Cabri Jr. allows pupils to form and verify conjectures.
Concord Consortium
Detective Stories
The truth will always come out. A short performance task has learners considering a witness statement given to a detective. They apply special line segments in triangles and Ceva's Theorem to prove that the witness is actually lying.
Curated OER
Angle Bisectors
Students identify different angles. In this geometry lesson plan, students identify different properties of triangles. They find the altitude, median and angle bisector.
Concord Consortium
In Oz We Tryst
The shortest distance from point A to point B is a straight line, but measuring distance gets more complicated when there are three points! Given the location of three friends, individuals determine the best point for all three friends...
Curated OER
Inscribing a Circle in a Triangle
Pupils investigate inscribing a circle in a triangle. They use Cabri Jr. to draw a triangle, locate the incenter, and use the distance from the incenter to a side of the triangle to inscribe a circle. The dynamic nature of the geometry...
Curated OER
Concurrent Lines in Triangles
Students explore the concept of concurrent lines in triangles. In this concurrent lines in triangles lesson, students work in groups to investigate properties of concurrent lines in acute, right, and obtuse triangles. Students use a...
Curated OER
Special Segments in Triangles
Young scholars identify important properties of triangles. In this geometry lesson, students differentiate between medians, bisectors and altitudes in a triangle. They identify the properties of these important segments.
Curated OER
Isosceles Triangles
Young scholars identify the properties of an isosceles triangle. In this geometry instructional activity, students find the midpoint, median and angle bisector of a triangle. They construct angle bisectors and measure missing angles.
Curated OER
Studying Special Segments in Triangles
Learners investigate special segments in triangles. In this geometry instructional activity, students graph, compare, estimate and predict findings based on their data. They differentiate between similarity and congruence of triangles.
Curated OER
Inscribed Angles
Students calculate the inscribed angle of a triangle. For this geometry lesson, students identify the angle created by intersection of a triangle and a circle. They see the relationship between the arc and the angle.
Curated OER
Special Triangles and Circles
Students investigate special triangles and circles. In this geometry instructional activity, students construct a perpendicular bisector and discuss angles of a triangle. They find the angle bisectors, vetex and the types of circle...
Curated OER
Hospital Locator
Pupils apply properties of triangles to the real world. In this geometry lesson, students identify the median and angle bisectors of triangles. They plan the appropriate are to place a new medical center based on their knowledge of...
Curated OER
Incenter of a Triangle
Tenth graders find the incenter of a triangle. In this geometry instructional activity, 10th graders define the way to create an incenter with an angle bisector. They differentiate between incenter and incircle.
Curated OER
Investigating Trigonometric Ratios Through Similar Right Triangles
Students identify similar and congruent right triangles. In this geometry lesson, students use trigonometric ratios to identify missing sides and angles of a triangle. They differentiate similar and congruent triangles.
Curated OER
IGD: Perpendicular Bisector
Students draw perpendicular bisectors. In this perpendicular bisectors lesson, students identify the perpendicular bisector in a polygon. They use web tools to create and measure perpendicular bisectors. Students identify lines of...
Curated OER
Pedal Triangles
Students identify the properties and theorems of triangles. In this geometry lesson plan, students construct angle bisectors using a compass and straight edge. They identify triangular similarity and congruency.
Mathematics Vision Project
Circles: A Geometric Perspective
Circles are the foundation of many geometric concepts and extensions - a point that is thoroughly driven home in this extensive unit. Fundamental properties of circles are investigated (including sector area, angle measure, and...
Curated OER
Incenter of a Triangle
Tenth graders explore the properties of the incenter of a triangle. For this geometry lesson, 10th graders construct a triangle and the angle bisectors of each angle. The dynamic properties of Cabri Jr. allow students to locate and...
Curated OER
Investigating Trigonometric Ratios Through Similar Right Triangles.
49Students investigate the properties of right triangles. In this geometry lesson, students differentiate between similar and congruent triangles. They use the Pythagorean Theorem to find the missing angles and sides.
Curated OER
The Minimal Distance Point from the Vertices of a Triangle
Students calculate the distance from the vertex of a triangle to the center. In this geometry lesson, students find the shortest distance between a point and the vertex of a triangle. They relate this concept of distance to the real world.
Curated OER
Triangles with Collinear Circumcenters
Students identify the circumcenter of a triangle. In this geometry lesson, students construct a perpendicular bisector using a straight edge and a compass. They differentiate between triangles and collinear points.
Curated OER
Plenty of Pythagoras
Using a twelve foot knotted rope, learners form a 3-4-5 right triangle. Following a discussion of observations about the lengths of the sides of the triangle, students use grid paper, scissors and a centimeter ruler to draw and measure...
Curated OER
Cabri Jr. Perpendicular Bisector of a Chord
Your learners will construct the perpendicular bisector of a chord. They use Cabri Jr. to construct a circle and a perpendicular bisector of a chord. They then measure lengths of the chords and perpendicular bisectors. Learners use...