Chapter 1 ยท ICSE Class 9 Mathematics (Selina Concise)

Rational & Irrational Numbers

Distinguish rational from irrational numbers, represent them on the number line, and simplify surds.

๐Ÿ”ข Chapter 1

Rational and irrational numbers placed on a number line A number line showing rational numbers like 1/2 and 3 as solid dots, and irrational numbers like the square root of 2 and pi as hollow dots, all sharing the same number line 1/2 โˆš2 3 ฯ€ โ— Rational โ—‹ Irrational
1.1

Identifying Rational and Irrational Numbers

A rational number can be written as p/q where p and q are integers and qโ‰ 0. An irrational number cannot be expressed this way โ€” its decimal expansion is non-terminating and non-repeating.

1

Is โˆš16 rational or irrational?

โˆš16=4, which is rational since it's a whole number

2

Is โˆš7 rational or irrational?

Irrational, since 7 is not a perfect square and its decimal expansion never terminates or repeats

3

Is 0.333... (recurring) rational or irrational?

Rational, since it equals 1/3 exactly, a ratio of two integers

1.2

Simplifying Surds

A surd is an irrational root that can't be simplified to remove the root entirely. Surds can be simplified by factoring out perfect square factors.

1

Simplify โˆš50.

โˆš50=โˆš(25ร—2)=5โˆš2

2

Simplify โˆš72.

โˆš72=โˆš(36ร—2)=6โˆš2

3

Simplify โˆš200.

โˆš200=โˆš(100ร—2)=10โˆš2

Practice

Exercises

1. Is โˆš25 rational or irrational?

2. Is ฯ€ rational or irrational?

3. Simplify โˆš48.

4. Simplify โˆš98.

5. Rationalize the denominator: 1/โˆš3

6. Is โˆš36 rational or irrational?

7. Is 0.1010010001... (non-repeating) rational or irrational?

8. Simplify โˆš125.

9. Simplify โˆš180.

10. Rationalize the denominator: 5/โˆš5