Study Guides/Maths/Every Irrational Number is a Real Number
Study Guide Β· Maths

Is Every Irrational Number a Real Number?

This statement is a classic 'True or False' question found in the very first exercise of the Class 9 NCERT Mathematics textbook (Number Systems). To answer it, we must understand the family tree of numbers.

Question (Click to Flip)

What is an imaginary number?

Answer

If a number is NOT a real number, it is an 'Imaginary' or 'Complex' number. This happens when you try to find the square root of a negative number (like $\sqrt{-5}$), which cannot exist on a standard number line.

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Key Facts

The combination of all Rational numbers and all Irrational numbers put together forms the collection of Real numbers.

The opposite statementβ€”'Every real number is an irrational number'β€”is False, because a real number could also be a rational number like 4.

1. The Answer

Statement: Every irrational number is a real number. Answer: True.

2. Mathematical Reason (The Family Tree)

  • The Real Number System (denoted by $\mathbb{R}$) is the grand 'father' category of all numbers that can be plotted on a physical number line.
  • The Real Number System is strictly divided into exactly two child categories:
    1. Rational Numbers: Numbers that can be written as a simple fraction $p/q$ (e.g., $1/2, 5, -3, 0.75$).
    2. Irrational Numbers: Numbers that CANNOT be written as a fraction, and have endless, non-repeating decimals (e.g., $\sqrt{2}, \pi, \sqrt{3}$).
  • Because Irrational Numbers are born directly from the Real Number family, every single irrational number is, by definition, a part of the Real Number collection.

3. The Number Line Proof

A Real Number is defined as any number that has a specific, unique point on the number line. Even though irrational numbers like $\sqrt{2}$ (1.4142...) go on forever, we can geometrically plot their exact location on a number line using the Pythagoras theorem. Since it exists on the line, it is a real number.

Questions and Answers

What is an imaginary number?+

If a number is NOT a real number, it is an 'Imaginary' or 'Complex' number. This happens when you try to find the square root of a negative number (like $\sqrt{-5}$), which cannot exist on a standard number line.

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