Students learn that similar triangles have the same shape but different sizes — with equal angles and proportional sides — and use proportions and scale factors to find missing lengths, even measuring a tree by its shadow.
Students will be able to…
How can you measure the height of a tree, a building, or a mountain without ever climbing it? Similar triangles turn a shadow into a ruler.
Project each problem and have students use proportions and scale factors to find the missing length. The tool shows the setup.
Tap any phase to open the teacher moves and student actions.
How can a shadow tell you a tree’s height?
Teacher models.
Class uses Solve with Similarity.
Students apply similarity.
One problem.
Aligned to the Common Core State Standards for Mathematics (High School: Geometry).
Decide if two figures are similar using similarity transformations.
Establish the AA criterion for triangle similarity.
Use similarity criteria to solve problems and prove relationships.
Prove theorems about triangles using similarity.
Preview the three formative checks. Tap “Sample answer” to see what mastery looks like — hide them before you print for students.
Have students use the AA (angle-angle) criterion to prove two triangles are similar, then find missing sides. A printable similarity sheet is in the Math library.
Tap a card to flip it, then rate whether you knew it. Built from this lesson’s vocabulary.
A quick self-check with instant feedback, drawn from this lesson’s key terms.
A print-and-go review sheet with a built-in answer key. Tap “Show answer key” to reveal answers, or print the clean version for students.