# Clip 9/13: Standard 5: Use Appropriate Tools Strategically Using Quadrilaterals Part A

## Overview

*Mathematically proficient students consider the available tools when solving a mathematical problem. These tools might include pencil and paper, [or] concrete models... 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...*

In this clip, Humphreys closes day one of the Properties of Quadrilaterals lesson, and orients students to the second part of the investigation in which they will justify and prove their findings about the diagonals of the kites, saying “convince yourself, convince a friend, convince a skeptic” to describe for students the level of precision necessary to justify their conjectures. The students use definitions, postulates, and theorems to develop a proof about the diagonals of a quadrilateral and how they constrain the type of figure that is formed. Humphreys moves between groups, checking in on the progress students are making in developing their justifications. At the close of the period, she employs the resource manager to make sure all the manipulatives and materials are collected and stored.