Mathematics
Grade 8
15 min
Rational numbers: find the sign
Rational numbers: find the sign
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1
Introduction & Learning Objectives
Learning Objectives
Identify whether a given rational number is positive, negative, or zero.
Apply the rules for multiplying and dividing signed numbers to determine the sign of a product or quotient of rational numbers.
Determine the sign of a rational number raised to an integer power.
Analyze expressions involving multiple operations with rational numbers to predict the final sign.
Explain the sign of a rational number in various forms (fractions, decimals, mixed numbers).
Solve problems involving the sign of rational numbers in real-world contexts.
Ever wonder how meteorologists predict if the temperature will be above or below freezing? 🌡️ It often comes down to understanding positive and negative numbers!
In this lesson, you'll learn how to quickly determine if a...
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Key Concepts & Vocabulary
TermDefinitionExample
Rational NumberAny number that can be expressed as a fraction $\frac{p}{q}$, where $p$ and $q$ are integers and $q \neq 0$.$\frac{3}{4}$, $-0.5$, $7$ (which is $\frac{7}{1}$), $0$ (which is $\frac{0}{1}$).
Positive NumberA number greater than zero, located to the right of zero on a number line.$5$, $\frac{1}{2}$, $0.75$, $100$.
Negative NumberA number less than zero, located to the left of zero on a number line.$-3$, $-\frac{2}{3}$, $-1.2$, $-25$.
ZeroThe number that is neither positive nor negative. It is the origin on the number line.$0$, $\frac{0}{5}$.
NumeratorThe top number in a fraction, representing the number of parts being considered.In $\frac{-3}{4}$, the numerator is $-3$.
DenominatorThe bottom number in a fraction, representing the total number of equal p...
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Core Formulas
Sign of a Fraction
A fraction $\frac{p}{q}$ is positive if $p$ and $q$ have the same sign. It is negative if $p$ and $q$ have different signs.
This rule applies to fractions where the negative sign can be in the numerator, denominator, or in front of the fraction. For example, $\frac{-a}{b} = \frac{a}{-b} = -\frac{a}{b}$.
Multiplication and Division of Signed Rational Numbers
$(+\text{number}) \times (+\text{number}) = +\text{result}$
$(-\text{number}) \times (-\text{number}) = +\text{result}$
$(+\text{number}) \times (-\text{number}) = -\text{result}$
$(-\text{number}) \times (+\text{number}) = -\text{result}$
The same rules apply for division.
When multiplying or dividing two rational numbers, if their signs are the same, the result is positive. If their signs are...
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Sign Up Free to ContinueSample Practice Questions
Challenging
Given that $x$ is a negative rational number, what is the sign of the expression $x - x^2$?
A.Positive
B.Negative
C.Zero
D.Depends on the specific value of x
Challenging
If $\frac{a}{b}$ is a negative number and $\frac{b}{c}$ is a positive number, what must be the sign of $a \times c$?
A.Positive
B.Negative
C.Zero
D.Cannot be determined
Challenging
What is the sign of the product of the first 100 non-zero integers: $(1) \times (-2) \times (3) \times (-4) \times \dots \times (99) \times (-100)$?
A.Positive
B.Negative
C.Zero
D.It alternates
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