# Why is 9 not a square number?

Numbers that can be expressed as the square of an integer are called square numbers. For example, 4 is a square number because it can be expressed as 2^2. 9, however, is not a square number because there is no integer that can be squared to arrive at 9.

## Definition of a Square Number

In mathematics, a square number is the result of multiplying an integer by itself. For example:

• 2 x 2 = 4
• 3 x 3 = 9
• 4 x 4 = 16

So 4, 9, and 16 are all square numbers. More formally, if n is an integer, then n^2 is a square number. For example, 2 is an integer, and 2^2 (which equals 4) is a square number.

### Properties of Square Numbers

Square numbers have several interesting properties:

• The square root of a square number is an integer. For example, the square root of 9 is 3, which is an integer.
• When represented geometrically as a square, the length of each side is equal to the square root. For example, the square root of 4 is 2, and a square with sides of length 2 has an area of 4 square units.
• Every square number is evenly divisible by 1, itself, and some other integer. For example, 4 is divisible by 1, 4, and 2.
• The gaps between square numbers get larger as the numbers get bigger. For example, 1, 4, 9, 16…

These types of patterns and relationships are what make square numbers interesting to study in number theory and algebra.

## Why 9 is Not a Square Number

Now that we understand the definition and properties of square numbers, let’s look at why 9 does not fit the criteria.

For a number to be a perfect square, its square root must be an integer. But when you take the square root of 9, you get:

√9 = 3

The square root of 9 is 3, which is an integer. So at first glance, it seems like 9 should be a square number.

However, for 9 to truly qualify as a square number, there must exist some integer, that when squared, equals 9. Let’s try plugging in some integers:

• 1^2 = 1
• 2^2 = 4
• 3^2 = 9
• 4^2 = 16

As we can see, there is no integer when squared that equals 9 exactly. The two integers closest to it are 3 and 4:

• 3^2 = 9
• 4^2 = 16

While 3 squared equals 9, that would make 9 a perfect square, not just a square number. By definition, a square number must be the product of an integer multiplied by itself. Because there is no integer that can be squared to get 9 exactly, 9 does not qualify as a true square number.

## Conceptualizing 9 Geometrically

We can also think about square numbers geometrically. When represented as a square, the length of a side must be an integer, and the area must equal the square number.

For example, 4 has an integer side length of 2:

 2 2 2 2

And an area of 4 square units.

Let’s try drawing 9 as a square:

 3 3 3 3

The side length needs to be 3 to make the area equal 9. But because the side length isn’t an integer, this representation doesn’t work. Again, we’ve confirmed that 9 cannot be represented as a proper square number geometrically.

## Why Does 9 Not Qualify?

The key point is that while the square root of 9 is an integer, there is no integer that when squared equals 9 exactly. This violates the requirement for a number to be categorized as a square.

We can take this concept a step further. The difference between a square number and a perfect square is:

• Square number – product of an integer multiplied by itself
• Perfect square – a number that has an integer square root

So while 9 has an integer square root (3), it is not the product of an integer multiplied by itself. And withoutsatisfying this criteria, 9 cannot be considered a square number.

### Other Interesting Examples

There are a few other examples of numbers that are “almost” square numbers, but don’t quite qualify:

• 8 – Square root is 2.828…, not an integer
• 50 – Square root is 7.071…, not an integer
• 123 – No integer squared equals 123

Even though these numbers are very close to being perfect squares, the same logic applies – they violate the formal requirements and cannot be categorized as true square numbers.

## Summary

To summarize, there are a few key reasons why 9 is not considered a square number:

• There is no integer that can be squared to arrive at 9 exactly
• It fails the conceptual test of drawing a square with an integer side length and area of 9
• While its square root is an integer (3), 9 is not the product of an integer multiplied by itself
• It does not meet the formal definition of a square number, which requires an integer squared result

So in summary:

Square number criteria:

– Integer side length when represented geometrically as a square

– Product of an integer multiplied by itself

9 fails to meet this criteria because:

– No integer squared equals 9 exactly

– Side length of geometric square would be non-integer √9

While at first glance 9 seems like it should qualify as a square number, upon closer inspection it does not satisfy the formal mathematical definition. Hopefully this explanation makes clear why 9 just misses the mark and cannot be considered a true square number!

## Conclusion

In summary, 9 is not a square number because there exists no integer that when squared equals 9. For a number to be considered a square number, it must be the product of an integer multiplied by itself. The square root of 9 is 3, which is an integer. However, 3 squared equals 9, which makes 9 a perfect square but not a square number. Square numbers cannot have fractional or decimal side lengths. When trying to represent 9 graphically as a square, the side length must be √9 or 3, which is non-integer. This violates the geometric definition of a square number. While 9 has some properties of a perfect square, it fails to meet the formal criteria for a square number in multiple ways. Understanding why numbers that seem square actually aren’t, like 9, provides great insight into foundational mathematical definitions and proofs.