Number System
Gujarat Board · Class 9 · Mathematics
Flashcards for Number System — Gujarat Board Class 9 Mathematics. Quick Q&A cards covering key concepts, definitions, and formulas.
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What is a rational number? Give the mathematical definition.
Answer
A number 'r' is called a rational number if it can be written in the form p/q, where p and q are integers and q ≠ 0. Examples: 1/2, -3/4, 5 (which is 5/1), 0 (which is 0/1).
What is an irrational number? Give the definition and examples.
Answer
A number 's' is called irrational if it cannot be written in the form p/q, where p and q are integers and q ≠ 0. Examples: √2, √3, √15, π, 0.10110111011110...
True or False: Every integer is a rational number. Justify your answer.
Answer
True. Every integer m can be expressed in the form m/1, where both m and 1 are integers and 1 ≠ 0. Therefore, every integer is a rational number.
What are the two types of decimal expansions that rational numbers can have?
Answer
Rational numbers have either: 1) Terminating decimal expansions (like 7/8 = 0.875), or 2) Non-terminating recurring (repeating) decimal expansions (like 1/3 = 0.333... = 0.3̄).
What type of decimal expansion do irrational numbers have?
Answer
Irrational numbers have non-terminating non-recurring (non-repeating) decimal expansions. For example, √2 = 1.4142135... and π = 3.14159265...
Express 0.6̄ (0.666...) in the form p/q.
Answer
Let x = 0.6̄ = 0.666... 10x = 6.666... 10x = 6 + 0.666... = 6 + x 10x - x = 6 9x = 6 x = 6/9 = 2/3…
What is the collection of real numbers denoted by, and what does it include?
Answer
The collection of real numbers is denoted by R. It includes all rational numbers and all irrational numbers together. Every point on the number line represents a unique real number.
If you add a rational number and an irrational number, what type of number do you get?
Answer
The sum of a rational number and an irrational number is always irrational. For example, 2 + √3 is irrational because √3 has a non-terminating non-recurring decimal expansion.
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