Rational and Irrational Numbers
ICSE · Class 9 · Mathematics
Flashcards for Rational and Irrational Numbers — ICSE Class 9 Mathematics. Quick Q&A cards covering key concepts, definitions, and formulas.
What is a rational number? Give the mathematical definition.
Answer
A rational number is a number that can be expressed as a/b, where 'a' and 'b' are both integers and 'b' ≠ 0. The set of rational numbers is denoted by Q. Examples: 3/4, -5/7, 0, 2 (which is 2/1).
What are the three conditions for a number a/b to be in its simplest rational form?
Answer
(i) b ≠ 0 (ii) a and b have no common factor other than 1 (they are co-primes) (iii) b is usually positive, while a may be positive, negative, or zero.
How do you insert n rational numbers between two given rational numbers x and y (where x < y)?
Answer
Step 1: Find d = (y-x)/(n+1). Step 2: The n rational numbers are: x+d, x+2d, x+3d, ..., x+nd. Example: To insert 2 numbers between 1 and 4: d = (4-1)/(2+1) = 1, so numbers are 2 and 3.
What is a terminating decimal? Give examples.
Answer
A terminating decimal is a decimal representation that ends after a finite number of digits. Examples: 1/8 = 0.125, 1/25 = 0.04, 3.4. These occur when division gives an exact result with no remainder.
What is a recurring or periodic decimal? How is it represented?
Answer
A recurring decimal is a non-terminating decimal where a digit or set of digits repeats continuously. Notation: A bar or dot is placed over the repeating part. Examples: 4/9 = 0.4̅ = 0.4444..., 4/7 =
When does a rational number a/b (in lowest terms) have a terminating decimal representation?
Answer
A rational number a/b has a terminating decimal if and only if the denominator b can be expressed as 2ᵐ × 5ⁿ, where m and n are whole numbers. Examples: 17/50 terminates because 50 = 2¹ × 5², but 23/7
Convert the recurring decimal 0.47̅ to a rational number.
Answer
Let x = 0.47̅ = 0.474747... Since 2 digits repeat, multiply by 100: 100x = 47.474747... Subtract: 100x - x = 47.474747... - 0.474747... → 99x = 47 → x = 47/99. Therefore, 0.47̅ = 47/99.
What is an irrational number? Give examples.
Answer
An irrational number is a real number that cannot be expressed as a/b where a and b are integers and b ≠ 0. It has a non-terminating, non-recurring decimal representation. Examples: √2 = 1.414213...,
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