1. 2.1 Find Square Roots and Compare Real Numbers
You will find square roots and compare real numbers.
Essential Questions
How do you evaluate a
square root and compare
real numbers?

2. Evaluate the expression.
EXAMPLE 1
Find square roots
Evaluate the expression. a.  – + 36 = 6
The positive and negative square
are 6 and – 6.
roots of 36 b.  49 = 7
The positive square root of 49 is 7.
The negative square root of 4 is – 2. c.  4 – = 2

3. Evaluate the expression.
EXAMPLE 1
GUIDED PRACTICE
Find square roots
for Example 1
Evaluate the expression.  – 1. 9 – = 3 2. 25  = 5  64 3. – + = 8 – +  – 4. 81 = 9 –

4. Approximate a square root
EXAMPLE 2
Approximate a square root
FURNITURE
The top of a folding table is a square whose area is 945 square inches. Approximate the side length of the
tabletop to the nearest inch.
SOLUTION 2 =
You need to find the side length s of the tabletop such that s This means that s is the positive square root of 945. You can use a table to determine whether 945 is a perfect square.

5. Approximate a square root Number 28 29 30 31 32 Square of number 784
EXAMPLE 2
Approximate a square root
Number 28 29 30 31 32
Square of number
784
841
900
961
1024
As shown in the table, 945 is not a perfect square. The greatest perfect square less than 945 is 900. The least perfect square greater than 945 is 961.
900 < 945 < 961
Write a compound inequality that compares 945 with both 900 and 961.
< 
961
900
945
Take positive square root of each number. 30 
945
< 31
Find square root of each perfect square.

6. EXAMPLE 2
Approximate a square root
The average of 30 and 31 is 30.5 and (30.5)2 = Because 945 > , is closer to 31 than 30.
ANSWER
The side length of the tabletop is about 31 inches.

7. Approximate the square root to the nearest integer.
EXAMPLE 2
GUIDED PRACTICE
Approximate a square root
for Example 2
Approximate the square root to the nearest integer. 5.  32 6 6. 
103 10 7.  48 –
– 7 8. 
350 –
– 19

8. EXAMPLE 3 Classify numbers
Tell whether each of the following numbers is a real number, a rational number, an irrational number, an integer, or a whole number: , , –  24 81
100 No
Yes
Real Number?
Whole Number?
Integer?
Irrational Number?
Rational Number?
Number  24
100
–  81

9. EXAMPLE 4
Graph and order real numbers ,
Order the numbers from least to greatest: 4 3 –  5 13
–2.5 9 .
SOLUTION
Begin by graphing the numbers on a number line. 4 3
ANSWER
Read the numbers from left to right:
–2.5, –  5 9 13 . ,

10. EXAMPLE 4
GUIDED PRACTICE
Graph and order real numbers
for Examples 3 and 4
Tell whether each of the following numbers is a real number, a rational number, an irrational number, an integer, or a whole number: , 5.2, 0, , 4.1,
Then order the numbers from least to greatest. 9.  7 9 2 –
–  20 9 2 – ,  7 20
4.1
5.2.
ANSWER

11. Graph and order real numbers for Examples 3 and 4
GUIDED PRACTICE
Graph and order real numbers
for Examples 3 and 4 No
Yes
Real Number?
Whole Number?
Integer?
Irrational Number?
Rational Number?
Number  20 7 9 2
4.1 –
5.2

12. EXAMPLE 5
Rewrite a conditional statement in if-then form
Rewrite the given conditional statement in if-then form. Then tell whether the statement is true or false. If it is false, give a counterexample.
SOLUTION a.
Given: No integers are irrational numbers.
If-then form: If a number is an integer, then it is not an irrational number.
The statement is true.

13. EXAMPLE 5
Rewrite a conditional statement in if-then form b.
Given: All real numbers are rational numbers.
If-then form: If a number is a real number, then it is a rational number.
The statement is false. For example, is a real number but not a rational number.  2

14. EXAMPLE 5
GUIDED PRACTICE
Rewrite a conditional statement in if-then form
for Example 5
Rewrite the given conditional statement in if-then form. Then tell whether the statement is true or false. If it is false, give a counterexample.
All square roots of perfect squares are rational
numbers.
10.
If-then form: If a number is the square root of perfect square, then it is a rational number.
The statement is true.

15. EXAMPLE 5
GUIDED PRACTICE
Rewrite a conditional statement in if-then form
for Example 5
Rewrite the given conditional statement in if-then form. Then tell whether the statement is true or false. If it is false, give a counterexample.
All repeating decimals are irrational numbers.
11.
If-then form: If a number is a repeating decimal, then it is an irrational number.
The statement is false. For example, 0.333… is a repeating decimal and can be written as , so it is a rational number. 1 3

16. EXAMPLE 5
GUIDED PRACTICE
Rewrite a conditional statement in if-then form
for Example 5
Rewrite the given conditional statement in if-then form. Then tell whether the statement is true or false. If it is false, give a counterexample.
No integers are irrational numbers.
12.
If-then form: If a number is an integer, then it is not an irrational number.
The statement is true.

17. Evaluate the expression.
Daily Homework Quiz
Evaluate the expression. 1. – + 
289
ANSWER – + 17 2.  36 –
ANSWER 3 16
Approximate the square root to the nearest integer. 3.  21 –

18. Daily Homework Quiz
ANSWER
– 5 4. 
620
ANSWER 25
A square courtyard has an area of 272 square feet. What is the side length of the courtyard to the nearest foot? 5.
ANSWER
16 ft

19. You will find square roots and compare real numbers.
Essential Questions
How do you evaluate a
square root and compare
real numbers?
All positive numbers have a positive and a negative square root.
Square roots of positive integers or rational numbers that are not perfect squares are irrational numbers that can be approximated by nonrepeating decimals.
To evaluate the square root of a, you need to find the number b such that b2 = a. To compare real numbers, you can graph the numbers on a number line, suing approximations for any square roots that are irrational numbers.