ALEX Lesson Plans
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Title: Proofs into Practice: The Pythagorean Theorem in the Real World
Description:
The introduction of this lesson has students verifying the famous Pythagorean Theorem with a handson proof. Students will then apply the Theorem in one of two ways: by solving for the side lengths of a right triangle and by determining whether three side lengths could possibly form a right triangle. Finally, students will choose one of two reallife applicataions to explore, using the Pythagorean Theorem.
Standard(s): [MA2015] GEO (912) 21: Use trigonometric ratios and the Pythagorean Theorem to solve right triangles in applied problems.* [GSRT8]
Subject: Mathematics (8  12)
Title: Proofs into Practice: The Pythagorean Theorem in the Real World
Description: The introduction of this lesson has students verifying the famous Pythagorean Theorem with a handson proof. Students will then apply the Theorem in one of two ways: by solving for the side lengths of a right triangle and by determining whether three side lengths could possibly form a right triangle. Finally, students will choose one of two reallife applicataions to explore, using the Pythagorean Theorem.
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Title: Geometric Mean and Indirect Measurement
Description:
In this inquirybased lesson, students will work in groups to gather measurements needed to approximate the height of a building. Students will discover how geometric mean can be used to find the lengths of missing sides of right triangles.
This lesson plan was created by exemplary Alabama Math Teachers through the AMSTI project.
Standard(s): [MA2015] GEO (912) 21: Use trigonometric ratios and the Pythagorean Theorem to solve right triangles in applied problems.* [GSRT8]
Subject: Mathematics (9  12)
Title: Geometric Mean and Indirect Measurement
Description: In this inquirybased lesson, students will work in groups to gather measurements needed to approximate the height of a building. Students will discover how geometric mean can be used to find the lengths of missing sides of right triangles.
This lesson plan was created by exemplary Alabama Math Teachers through the AMSTI project.
Thinkfinity Lesson Plans
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Title: The Triangle Inequality
Description:
In this reproducible activity, from an Illuminations lesson, students investigate how three sides can be arranged to make both triangles and nontriangles.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: The Triangle Inequality
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
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Title: Inequalities in Triangles
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.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: Inequalities in Triangles
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
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Title: Pieces of Proof
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.
Standard(s): [MA2015] GEO (912) 18: Use congruence and similarity criteria for triangles to solve problems and to prove relationships in geometric figures. [GSRT5]
Subject: Mathematics Title: Pieces of Proof
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
Thinkfinity Learning Activities
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Title: Half Angle
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.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: Half Angle
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
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Title: IGD: Area of a Triangle
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.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: IGD: Area of a Triangle
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
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Title: IGD: Median
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.
Standard(s): [MA2015] GEO (912) 26: Construct the inscribed and circumscribed circles of a triangle, and prove properties of angles for a quadrilateral inscribed in a circle. [GC3]
Subject: Mathematics Title: IGD: Median
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
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Title: IGD: Simson Line
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.
Standard(s): [MA2015] MI1 (912) 11: Describe the development of mathematical tools and their applications. (Alabama)
Subject: Mathematics Title: IGD: Simson Line
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
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Title: Isosceles Triangle Investigation
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.
Standard(s): [MA2015] ALT (912) 33: Write a function that describes a relationship between two quantities.* [FBF1]
Subject: Mathematics Title: Isosceles Triangle Investigation
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
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Title: Triangle Classification
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.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: Triangle Classification
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
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Title: Triangle Island
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.
Standard(s): [MA2015] GEO (912) 17: Prove theorems about triangles. Theorems include a line parallel to one side of a triangle divides the other two proportionally, and conversely; and the Pythagorean Theorem proved using triangle similarity. [GSRT4]
Subject: Mathematics Title: Triangle Island
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

