Squares and Square Roots
The square of a number?
When we multiply an integer by itself we call the
product
the square of the number.
For example: 4 x 4 = 16
The square of 4 is 16
The pictures above show
why we call these products squares.
Squared Numbers
The examples below show how squares can be found.
| Number | Multiplied by itself | Square |
| 1 | 1 x 1 | 1 |
| 2 | 2 x 2 | 4 |
| 3 | 3 x 3 | 9 |
| 4 | 4 x 4 | 16 |
| 5 | 5 x 5 | 25 |
| 6 | 6 x 6 | 36 |
| 7 | 7 x 7 | 49 |
| 8 | 8 x 8 | 64 |
| Number | Multiplied by itself | Square |
| 9 | 9 x 9 | 81 |
| 10 | 10 x 10 | 100 |
| 11 | 11 x 11 | 121 |
| 12 | 12 x 12 | 144 |
| 13 | 13 x 13 | 169 |
| 14 | 14 x 14 | 196 |
| 15 | 15 x 15 | 225 |
Squared Words!
You'll hear different words used when people talk about squares. e.g.
- Square of a number: 25 is the square of 5
- Squaring a number: multiplying the number by itself
- A squared number: 100 is a square number
- 3 squared: 3 squared is 9
- What's the square of 9? The square of 9 is 81
- Perfect square: Perfect square is another term for square number
Make sure your children know the short way of finding a square on a calculator. e.g. to find 6 x 6, enter 6, x, =
Writing squares
Squares are powers of two.
We write squares using the same notation that we use with other powers.
e.g. for 3 squared (or 3 x 3)
we write
32
We could talk about 3 to the power of 2, or the second power of three but we don't usually do so; we say 3 squared. We write 32
Square Roots
You can think of finding square roots as the opposite of finding squares. You find the square root of a number (let's call it number A) by finding the number that, when multiplied by itself produces number A. The examples below show this:
| Number | Square Root | |
1 x 1 = |
1 | 1 |
2 x 2 = |
4 | 2 |
3 x 3 = |
9 | 3 |
4 x 4 = |
16 | 4 |
5 x 5 = |
25 | 5 |
6 x 6 = |
36 | 6 |
7 x 7 = |
49 | 7 |
8 x 8 = |
64 | 8 |
| Number | Square Root | |
9 x 9 = |
81 | 9 |
10 x 10 = |
100 | 10 |
11 x 11 = |
121 | 11 |
12 x 12 = |
144 | 12 |
13 x 13 = |
169 | 13 |
14 x 14 = |
196 | 14 |
15 x 15 = |
225 | 15 |
16 x 16 = |
256 | 16 |
Note: Think of these examples: 4 x 4 = 16 and - 4 x - 4 = 16.
Positive numbers
have two square roots; a positive (called the principal
square root) and a negative. Unless you are asked for the negative
square root, you can just give the principal square root.
When exploring squares and square roots with your children, emphasize that each process is the inverse of the other. In other words, one undoes the other.
Writing Square Roots
Make sure that your children know the square root symbol and that they can find and use it on a calculator.
Calculating and Estimating Square Roots
Most calculators have a square root button that quickly calculates square roots. There are other ways of calculating square roots but they aren't quick. If you need an approximate value for a square root you can use a method like the one below.
| What is the square root of 42? | |||
| What two squares does 42 come between? | 36 and 49 | ||
| What are the square roots of 36 and 49 | 6 and 7 | ||
| So the square root of 42 is between
6 and 7. Let's use some trial and error to get an approximate answer. |
|||
| Let's try 6.5 | 42 ÷ 6.5 = 6.46 | ||
| We're looking to get the number we divide
by to be as close to the answer we get as possible. In this case
we have 6.5 and 6.46 Close, but we can get closer. |
|||
| Let's take the average of 6.5 and 6.46 and try that. | 42 ÷ 6.48 = 6.48 | ||
| So we have an square root that is accurate to two decimal places. You can repeat these steps to get as accurate an answer as you want. | |||
Squares and Square Roots Charts
There are two square number charts, both shown above. You will find the printable version of the one on the left here and the 12 to 152 one on the right here.
