Åk 6–9

English/عربي

2.1 The Unknown Number
An equation is an equality between two sides. Those two sides are divided by an equal sign (=).

The numbers on those sides can be written out if you know what they are.

Here is an example:
 Left Hand Side  (LHS) Right Hand Side (RHS)
 4 + 2 = 7 - 1 Four plus two is sex = Seven minus one is also six 6 = 6

The two sides are equal.

If we leave out a number on either side, we can figure out what that number should be.

Example:

A) 7 + __ = 10

Here you can probably see that it should be 3 which has been left out because

7 + 3 = 10

B) 8 - __ = 3
Here you can see that it should be 5 which has been left out because

8 – 5 = 3

We replace the space with a question mark instead.

4 + ? = 12

What should be there instead of the question mark?

Here you should be able to figure out that it will be an 8 instead of the question mark:

4 + 8 = 12

We replace the question mark with an eight.. ? = 8

In equations instead of using spaces or question marks, you usually use other signs, normally letters for the unknown numbers. Often x, y, or z is used because there are letters not often seen in writings.

3 + x = 9

3 + 6 = 9

We replace the letter x with a sex so that the equality is correct.  We can therefore say that in this case x = 6. x is even called a root of the equation.