Illustrative Mathematics
Running Around a Track II
On your mark, get set, GO! The class sprints toward the conclusions in a race analysis activity. The staggered start of the 400-m foot race is taken apart in detail, and then learners step back and develop some overall race strategy...
Illustrative Mathematics
The Lighthouse Problem
Long considered the symbol of safe harbor and steadfast waiting, the lighthouse gets a mathematical treatment. The straightforward question of distance to the horizon is carefully presented, followed by a look into the...
Illustrative Mathematics
Running Around a Track I
The accuracy required by the design and measurement of an Olympic running track will surprise track stars and couch potatoes alike. Given a short introduction, the class then scaffolds into a detailed analysis of the exact nature of the...
Illustrative Mathematics
How Thick Is a Soda Can I?
The humble soda can gets the geometric treatment in an activity that links math and science calculations. After a few basic assumptions are made and discussed, surface area calculations combine with density information to develop an...
Illustrative Mathematics
Bank Shot
Young geometers become pool sharks in this analysis of the angles and lengths of a trick shot. By using angles of incidence and reflection to develop similar triangles, learners plan the exact placement of balls to make the shot....
Illustrative Mathematics
Are They Similar?
Learners separate things that just appear similar from those that are actually similar. A diagram of triangles is given, and then a variety of geometric characteristics changed and the similarity of the triangles analyzed. Because the...
Illustrative Mathematics
Toilet Roll
Potty humor is always a big hit with the school-age crowd, and potty algebra takes this topic to a whole new level. Here the class develops a model that connects the dimensions (radii, paper thickness, and length of paper) of a...
Illustrative Mathematics
How Many Cells Are in the Human Body?
Investigating the large numbers of science is the task in a simple but deep activity. Given a one-sentence problem set-up and some basic assumptions, the class sets off on an open-ended investigation that really gives some...
Illustrative Mathematics
Seven Circles III
A basic set-up leads to a surprisingly complex analysis in this variation on the question of surrounding a central circle with a ring of touching circles. Useful for putting trigonometric functions in a physical context, as well as...
Illustrative Mathematics
Joining Two Midpoints of Sides of a Triangle
Without ever using the actual term, this exercise has the learner develop the key properties of the midsegment of a triangle. This task leads the class to discover a proof of similar triangles using the properties of parallel...
Illustrative Mathematics
Similar Triangles
Proving triangles are similar is often an exercise in applying one of the many theorems young geometers memorize, like the AA similarity criteria. But proving that the criteria themselves are valid from basic principles is a great...
Illustrative Mathematics
Shortest Line Segment from a Point P to a Line L
One of the hardest skills for many young geometers to grasp is to move beyond just declaring obvious things true, and really returning to fundamental principles for proof. This brief exercise stretches those proving muscles as the...
Illustrative Mathematics
Accuracy of Carbon 14 Dating II
The scientific issue of carbon-14 dating and exponential decay gets a statistics-based treatment in this problem. The class starts with a basic investigation of carbon content, but then branches out to questions of accuracy and...
Illustrative Mathematics
Coins in a Circular Pattern
What starts as a basic question of division and remainders quickly turns abstract in this question of related ratios and radii. The class works to surround a central coin with coins of the same and different values, then develops a...
Illustrative Mathematics
How Thick Is a Soda Can II?
Science, technology, and math come together in this one combination exercise. Analyzing the common soda can from both a purely mathematical perspective and a scientific angle allows for a surprisingly sophisticated comparison of...
Illustrative Mathematics
Extensions, Bisections and Dissections in a Rectangle
Gaining practice in translating a verbal description into a diagram and then an equation is the real point of this similar triangles exercise. Once the diagram is drawn, multiple methods are provided to reach the conclusion. An effective...
Illustrative Mathematics
Eratosthenes and the Circumference of the Earth
The class gets to practice being a mathematician in ancient Greece, performing geometric application problems in the way of Eratosthenes. After following the steps of the great mathematicians, they then compare the (surprisingly...
Illustrative Mathematics
Tilt of Earth's Axis and the Four Seasons
Geometry meets earth science as high schoolers investigate the cause and features of the four seasons. The effects of Earth's axis tilt features prominently, along with both the rotation of the earth about the axis and its orbit...
Illustrative Mathematics
Regular Tessellations of the Plane
Bringing together the young artists and the young organizers in your class, this lesson takes that popular topic of tessellations and gives it algebraic roots. After covering a few basic properties and definitions, learners attack the...
Illustrative Mathematics
Two Wheels and a Belt
Geometry gets an engineering treatment in an exercise involving a belt wrapped around two wheels of different dimensions. Along with the wheels, this belt problem connects concepts of right triangles, tangent lines, arc length, and...
Illustrative Mathematics
Placing a Fire Hydrant
Triangle centers and the segments that create them easily become an exercise in memorization, without the help of engaging applications like this lesson. Here the class investigates the measure of center that is equidistant to the three...
Illustrative Mathematics
Why Does SSS Work?
While it may seem incredibly obvious to the geometry student that congruent sides make congruent triangles, the proving of this by definition actually takes a bit of work. This exercise steps the class through this kind of proof by...
Illustrative Mathematics
How Many Leaves on a Tree? (Version 2)
A second attack at figuring out the number of leaves on a tree, this activity makes both an excellent follow-up to version 1 and a stand-alone activity. Learners practice setting parameters and deciding acceptable estimate precision, and...
Illustrative Mathematics
How Many Leaves on a Tree?
This is great go-to activity for those spring or fall days when the weather beckons your geometry class outside. Learners start with a small tree, devising strategies to accurately estimate the leaf count. They must then tackle the...