Mathematics
Grade 8
15 min
Reciprocals and multiplicative inverses
Reciprocals and multiplicative inverses
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1
Introduction & Learning Objectives
Learning Objectives
Identify the reciprocal of a given rational number.
Define a multiplicative inverse and explain its relationship to a reciprocal.
Calculate the reciprocal of positive and negative integers, fractions, and mixed numbers.
Apply the concept of reciprocals to rewrite division problems as multiplication problems.
Verify that a number and its reciprocal multiply to 1.
Solve problems involving reciprocals in the context of rational numbers.
Ever wonder how dividing by a fraction is like multiplying by its 'flip'? 🤔 Let's uncover the secret to turning tricky division into easy multiplication!
In this lesson, you'll learn about reciprocals and multiplicative inverses, powerful tools that simplify operations with rational numbers. Understandin...
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Key Concepts & Vocabulary
TermDefinitionExample
ReciprocalThe number you multiply by another number to get a product of 1. For a fraction, it's found by flipping the numerator and denominator.The reciprocal of $\frac{2}{3}$ is $\frac{3}{2}$.
Multiplicative InverseAnother name for a reciprocal. It's the number that, when multiplied by a given number, results in the multiplicative identity (which is 1).The multiplicative inverse of 5 is $\frac{1}{5}$.
ProductThe result obtained when two or more numbers are multiplied together.The product of 4 and $\frac{1}{4}$ is 1.
Multiplicative IdentityThe number 1. When any number is multiplied by 1, the number itself does not change.$7 \times 1 = 7$.
Rational NumberAny number that can be expressed as a fraction $\frac{p}{q}$, where $p$ and $q$ are integers and $q$ is...
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Core Formulas
Reciprocal Property
For any non-zero rational number $a$, its reciprocal is $\frac{1}{a}$.
This rule states that to find the reciprocal of any number (except zero), you simply write 1 over that number.
Multiplicative Inverse Property
For any non-zero rational number $a$, $a \times \frac{1}{a} = 1$.
This rule shows that when a number is multiplied by its reciprocal (or multiplicative inverse), the product is always 1.
Reciprocal of a Fraction
For any non-zero fraction $\frac{a}{b}$, its reciprocal is $\frac{b}{a}$.
To find the reciprocal of a fraction, you simply 'flip' the fraction by swapping its numerator and denominator.
Division using Reciprocals
Dividing by a non-zero rational number is the same as multiplying by its reciprocal: $\frac{a}{b} \div...
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Challenging
If a non-zero rational number 'x' is between 0 and 1 (0 < x < 1), what must be true about its reciprocal, 1/x?
A.The reciprocal is also between 0 and 1.
B.The reciprocal is greater than 1.
C.The reciprocal is a negative number.
D.The reciprocal is equal to 0.
Challenging
What is the reciprocal of the reciprocal of -7/11?
A.1
B.11/7
C.-11/7
D.-7/11
Challenging
Solve for x in the equation: (x ÷ 2/3) = 9/4
A.27/8
B.8/27
C.3/2
D.6/4
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