# Lesson 1The Areas of Squares and Their Side Lengths

Let’s investigate the squares and their side lengths.

### Learning Targets:

• I can find the area of a tilted square on a grid by using methods like “decompose and rearrange” and “surround and subtract.”
• I can find the area of a triangle.

## 1.2Decomposing to Find Area

Find the area of each shaded square (in square units).

### Are you ready for more?

Any triangle with a base of 13 and a height of 5 has an area of .

Both shapes in the figure have been partitioned into the same four pieces. Find the area of each of the piece and verify the corresponding parts are the same in each picture. There appears to be one extra unit of area in the right figure than in the left one. If all of the pieces have the same area, how is this possible?

## 1.3Estimating Side Lengths from Areas

1. What is the side length of square A? What is its area?
2. What is the side length of square C? What is its area?
3. What is the area of square B? What is its side length? (Use tracing paper to check your answer to this.)
4. Find the areas of squares D, E, and F. Which of these squares must have a side length that is greater than 5 but less than 6? Explain how you know.

## 1.4Making Squares

Use the applet to determine the total area of the five shapes, , , , , and . Assume each small square is equal to 1 square unit.

## Lesson 1 Summary

The area of a square with side length 12 units is  or 144 units2.

The side length of a square with area 900 units2 is 30 units because .

Sometimes we want to find the area of a square but we don’t know the side length. For example, how can we find the area of square ?

One way is to enclose it in a square whose side lengths we do know.

The outside square has side lengths of 11 units, so its area is 121 units2. The area of each of the four triangles is , so the area of all four together is units2. To get the area of the shaded square, we can take the area of the outside square and subtract the areas of the 4 triangles. So the area of the shaded square is or 73 units2.

## Lesson 1 Practice Problems

1. Find the area of each square. Each grid square represents 1 square unit.

2. Find the length of a side of a square if its area is:

1. 81 square inches
2. cm2
3. 0.49 square units
4. square units
3. Find the area of a square if its side length is:

1. 3 inches
2. 7 units
3. 100 cm
4. 40 inches
5. units
4. Evaluate . Choose the correct answer:

5. Noah reads the problem, “Evaluate each expression, giving the answer in scientific notation.” The first problem part is: . Noah says, “I can rewrite as . Now I can add the numbers: .” Do you agree with Noah’s solution to the problem? Explain your reasoning.

6. Select all the expressions that are equivalent to .