# Lesson 2

Side Lengths and Areas

### Lesson Narrative

In this lesson, students learn about square roots. The warm-up helps them see a single line segment as it relates to two different figures: as a side length of a triangle and as a radius of a circle. In the next activity, they use this insight to estimate the side length of a square via a geometric construction that relates the side length of the square to a point on the number line, and verify their estimate using techniques from the previous lesson. Once students locate the side length of the square as a point on the number line, they are formally introduced to square roots and square root notation:

$$\sqrt{a}$$ is the length of a side of a square whose area is $$a$$ square units.

In the final activity, students use the graph of the function $$y = x^2$$ to estimate side lengths of squares with integer areas but non-integer side lengths.

### Learning Goals

Teacher Facing

• Comprehend the term “square root of $a$” (in spoken language) and the notation $\sqrt{a}$ (in written language) to mean the side length of a square whose area is $a$ square units.
• Create a table and graph that represents the relationship between side length and area of a square, and use the graph to estimate the side lengths of squares with non-integer side lengths.
• Determine the exact side length of a square and express it (in writing) using square root notation.

### Student Facing

Let’s investigate some more squares.

### Student Facing

• I can explain what a square root is.
• If I know the area of a square, I can express its side length using square root notation.
• I understand the meaning of expressions like $\sqrt{25}$ and $\sqrt{3}$.

Building On

Building Towards

### Glossary Entries

• square root

The square root of a positive number $$n$$ is the positive number whose square is $$n$$. It is also the the side length of a square whose area is $$n$$. We write the square root of $$n$$ as $$\sqrt{n}$$.

For example, the square root of 16, written as $$\sqrt{16}$$, is 4 because $$4^2$$ is 16.

$$\sqrt{16}$$ is also the side length of a square that has an area of 16.