# Clip 10/13: Standard 5: Use Appropriate Tools Strategically Using Quadrilaterals Part E

## Overview

*Mathematically proficient students consider the available tools when solving a mathematical problem. These tools might include pencil and paper, ...[or] a ruler. Proficient students are sufficiently familiar with tools appropriate for their grade or course to make sound decisions about when each of these tools might be helpful...*

Cathy Humphreys leads an extended exploration of a proof of the properties of quadrilaterals, helping students learn to investigate, formulate, conjecture, justify, and ultimately prove mathematical theorems. In this clip, Humphreys circulates around groups of students as they use rulers, protractors, and sheets of paper to make different kinds of quadrilaterals and examine and “guarantee” their properties. A group of students debates whether or not one student’s assertion about the properties of a trapezoid hold in all circumstances, using the kite “sticks” to illustrate their points. 9th/10th grade first video. This clip is also indicative of standard 1 (make sense of problems & persevere in solving them).