Multiplicative Inverse of a Number — Definition & Examples

Multiplicative Inverse of a Number
Reciprocal

The reciprocal of x is $The fraction 1 over x$ . In other words, a reciprocal is a fraction flipped upside down. Multiplicative inverse means the same thing as reciprocal.

For example, the multiplicative inverse (reciprocal) of 12 is $The fraction 1/12$ and the multiplicative inverse (reciprocal) of $The fraction 3/5, with 3 as the numerator and 5 as the denominator.$ is $The fraction 5 over 3$ .

Note: The product of a number and its multiplicative inverse is 1. Observe that $The fraction 3/5, with 3 as the numerator and 5 as the denominator.$ · $The fraction 5 over 3$ = 1.

See also

Inverse

Key Formula

x \cdot \frac{1}{x} = 1 \quad (x \neq 0)

Where:

$x$ = Any nonzero number whose multiplicative inverse you want to find
$\frac{1}{x}$ = The multiplicative inverse (reciprocal) of x

Worked Example

Problem: Find the multiplicative inverse of 7, and verify your answer.

Step 1: Write the multiplicative inverse. For any nonzero number, the multiplicative inverse is 1 divided by that number.

\text{Multiplicative inverse of } 7 = \frac{1}{7}

Step 2: Verify by multiplying the number and its inverse. The product must equal 1.

7 \cdot \frac{1}{7} = \frac{7}{7} = 1 \; \checkmark

Answer: The multiplicative inverse of 7 is

\frac{1}{7}

Another Example

Problem: Find the multiplicative inverse of the fraction

\frac{3}{5}

, and verify your answer.

Step 1: Flip the fraction. To find the reciprocal of a fraction, swap the numerator and denominator.

\text{Multiplicative inverse of } \frac{3}{5} = \frac{5}{3}

Step 2: Verify by multiplying the original fraction by its inverse.

\frac{3}{5} \cdot \frac{5}{3} = \frac{15}{15} = 1 \; \checkmark

Answer: The multiplicative inverse of

\frac{3}{5}

\frac{5}{3}

Frequently Asked Questions

Does 0 have a multiplicative inverse?

No. There is no number you can multiply by 0 to get 1, because 0 times anything is 0. This is why division by zero is undefined, and why the multiplicative inverse exists only for nonzero numbers.

What is the multiplicative inverse of a negative number?

The multiplicative inverse of a negative number is also negative. For example, the multiplicative inverse of

-4

\frac{1}{-4} = -\frac{1}{4}

, because

(-4) \cdot \left(-\frac{1}{4}\right) = 1

. The sign stays the same; only the magnitude is reciprocated.

Multiplicative Inverse vs. Additive Inverse

The multiplicative inverse of

x

\frac{1}{x}

, and their product equals 1. The additive inverse of

x

-x

, and their sum equals 0. Both "undo" an operation — the multiplicative inverse undoes multiplication, while the additive inverse undoes addition.

Why It Matters

Multiplicative inverses are the foundation of division. Dividing by a number is the same as multiplying by its reciprocal, so

a \div b = a \cdot \frac{1}{b}

. This idea is used constantly when solving equations — for instance, if

5x = 20

, you multiply both sides by

\frac{1}{5}

to isolate

x

. Reciprocals also appear in rates, proportions, and rational expressions throughout algebra and beyond.

Common Mistakes

Mistake: Confusing the multiplicative inverse with the additive inverse (thinking the inverse of 5 is −5).

Correction: The multiplicative inverse of 5 is

\frac{1}{5}

, not

-5

. Remember: multiplicative inverse × original number = 1, whereas additive inverse + original number = 0.

Mistake: Trying to find the multiplicative inverse of 0.

Correction: Zero has no multiplicative inverse. No number multiplied by 0 gives 1. Always check that the number is nonzero before finding its reciprocal.

Related Terms

Fraction — Reciprocals are fractions flipped upside down
Product — A number times its inverse has product 1
Inverse — General concept that includes multiplicative inverse
Reciprocal — Synonym for multiplicative inverse
Additive Inverse — The inverse that undoes addition instead
Division — Dividing equals multiplying by the reciprocal
Identity — 1 is the multiplicative identity produced by the inverse