Lesson Plan


Lesson Plans and Creative Activities for Geometry Classroom


  • Mathematics > General
  • Mathematics > Geometry

Education Levels:

  • Grade 9
  • Grade 10
  • Grade 11
  • Grade 12


geometry measurement coordinate conjecture pythagorean theorum trapezoid



Access Privileges:

Public - Available to anyone

License Deed:

Creative Commons Attribution 3.0


Update Standards?

CCSS.Math.Content.K.G.B.4: Common Core State Standards for Mathematics

Analyze and compare two- and three-dimensional shapes, in different sizes and orientations, using informal language to describe their similarities, differences, parts (e.g., number of sides and vertices/"corners") and other attributes (e.g., having sides of equal length).

CCSS.Math.Content.1.G.A.1: Common Core State Standards for Mathematics

Distinguish between defining attributes (e.g., triangles are closed and three-sided) versus non-defining attributes (e.g., color, orientation, overall size); build and draw shapes to possess defining attributes.

S2486466: Texas Essential Knowledge and Skills for Mathematics

distinguish between attributes that define a two-dimensional or three-dimensional figure and attributes that do not define the shape;
Curriki Rating
On a scale of 0 to 3
On a scale of 0 to 3

This resource was reviewed using the Curriki Review rubric and received an overall Curriki Review System rating of 3, as of 2009-07-25.

Component Ratings:

Technical Completeness: 3
Content Accuracy: 3
Appropriate Pedagogy: 3

Reviewer Comments:

This is something between a lesson plan and an exercise. It is a tough problem requiring insight, and the problem is fully worked out in the text.
Regis Smith
April 17, 2011

I only see one major problem with the "CircumCircle" lesson-- the triangle side lengths are mislabeled. I think Johnny Texas' review is a bit harsh and misleading, especially since his (Texas') third paragraph includes a mathematical error-- moving point A along the circumference of the circle does not change the measure of angle A, as long as angle A cuts out the same arc BC.

I think the "CircumCircle" lesson is a fine example of a special case of a well-known result. It shows students they do not have to automatically apply memorized formulas to every scenario. The typesetting could be improved, but that's just presentation.

Johnny Texas
April 28, 2010

This rating and comment only applies to the resource labeled "CircumCircle." Your problem (while interesting) is not solvable by your own presented solution.

First the triangle you present does not exist (the one you have for this very problem on your website is correct in that line segment AC should be 6.6cm). Furthermore if your solution is that the diameter of the circle circumscribing triangle ABC is 7cm then both points A and C can not lie on this circle as their line segment measures 7.2cm.

Furthermore the interior angle is twice the measure of its corresponding exterior angle as long as the angles measure the same arc of the circle AND share the diameter and the corresponding radius as one of their sides. What you have presented is completely illogical and frankly impossible because you could rotate point A around the circle and create many different angles which must equal the same angle when doubled according to your answer.

Please Please do not use this to teach math to students as you will just give them a greater hardship than they may begin with!

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