ALEX Lesson Plans
Subject: Mathematics (9  12) Title: What you know about the Bermuda Triangle?
Description: The basis of this lesson is for students to form a connection between the importance of geometry as it relates to the Bermuda Triangle. Students should think about the geographical locations and how they form a particular type of triangle. Within the triangle exists a relationship between the angles and the length of the sides. As the students reflect prior concepts and skills should come to mind to help them solve the problem. The ideas presented here can be used as the final lesson in a unit on triangles to summarize all that students have learned. Alternatively, the main problem from this lesson could be used as a final assessment activity for a unit on triangles.
This is a College and CareerReady Standards showcase lesson plan.
Subject: Mathematics (7  12) Title: Is it a Triangle?
Description: The purpose of this lesson is to help students investigate the relationships of the lengths of the sides of a triangle in order to discover the three triangle inequality theorems. Students will learn how to draw valid conclusions from the information obtained from the activity and apply those conclusions to real world geometry problems. This serves as an introduction into more advanced geometric theorems. This lesson plan was created as a result of the Girls Engaged in Math and Science, GEMS Project, funded by the Malone Family Foundation.
Subject: Mathematics (9  12) Title: Investigation of Special Segments of Triangles
Description: This lesson will enable students to investigate three special segments of triangles in a very concrete way. The students will fold paper triangles to create the segments. This lesson would be a great way for students to explore the properties of the segments and their intersections.
Thinkfinity Lesson Plans
Subject: Mathematics Title: The Triangle Inequality
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Description: In this reproducible activity, from an Illuminations lesson, students investigate how three sides can be arranged to make both triangles and nontriangles. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: IGD: Euler Line
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Description: This student interactive, from Illuminations, helps students understand and investigate Euler lines. Students read a definition and then construct the Euler line of a triangle using the interactive tool. They learn that the Euler line involves three points associated with triangles: the circumcenter, orthocenter, and centroid. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Inequalities for Sides and Angles
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Description: This reproducible activity sheet, from an Illuminations lesson, guides students as they examine the relationship between the locations of sides and angles in a triangle. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Triangle Island
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Description: This student interactive, from an Illuminations lesson, allows students to explore the distances from an interior point of a polygon to its sides and determine the sum of these distances. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Triangle Classification
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Description: This student interactive, from an Illuminations lesson, allows students to turn a segment into a right triangle, an isosceles triangle, and an obtuse triangle. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: IGD: Area of a Triangle
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Description: This student interactive, from Illuminations, helps students understand and investigate how to find the area of a triangle by finding a way to make it look like a simpler shapone whose area formula is known. Students make a copy of the triangle, and then make a parallelogram using the triangle and its copy. Students then determine that the area of the triangle is onehalf that of the parallelogram. Thinkfinity Partner: Illuminations Grade Span: 3,4,5,6,7,8
Subject: Mathematics Title: IGD: Median
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Description: This student interactive, from Illuminations, helps students understand and investigate the median of a triangle. Students read a definition and then use the interactive tool to manipulate and explore the properties of triangle medians by changing the shape of a triangle. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Hospital Locator
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Description: In this Illuminations lesson, students begin with a problem in a realworld context to motivate the need to construct circumcenters and then incenters of triangles. Students must make sense of these constructions in terms of bisecting sides and angles. There are links to student interactives and other resources. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: IGD: Simson Line
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Description: This student interactive, from Illuminations, helps students understand and investigate a triangle s Simson line, which is the line passing through the feet of the perpendiculars dropped from P to the three sides of a triangle. Students construct the Simson line for a given triangle using the interactive applet. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Isosceles Triangle Investigation
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Description: This student interactive, from an Illuminations lesson, allows students to investigate the relationship between the area of the triangle and the length of its base. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Pieces of Proof
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Description: This lesson offers an intermediate step of putting together the statements and reasons to build a formal geometry proof. There is a leap to be made from understanding postulates and theorems in geometry to writing proofs using them. Students are given the parts of the proof and have to put them in a correct order, like a puzzle, rather than starting with a blank page to generate the statements and reasons themselves. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Half Angle
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Description: This student interactive, from an Illuminations lesson, allows students to find the incenter of a triangle and see a visual explanation of why it occurs where it does. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Inequalities in Triangles
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Description: In this Illuminations lesson, students use pasta to create models of triangles and nontriangles in order to investigate the relationship between the longest side of the triangle and the sum of the other two sides of the triangle. In addition, students measure the sides and angles of a scalene triangle and investigate the relationship between the location of the largest angle and largest side in a triangle. There are also links to online activity sheets. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Hospital Locator
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Description: In this student interactive, from an Illuminations lesson, students act as community planners, trying to place a new medical center equidistant from three cities. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12
Subject: Mathematics Title: Beyond Triangula Island
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Description: Using this reproducible activity sheet, from an Illuminations lesson, students record their findings as they measure distances from interior points to sides of an equilateral triangle, a square, an octagon and a hexagon. Students answer questions based on their findings. Thinkfinity Partner: Illuminations Grade Span: 9,10,11,12

