Introduction to Algebra

What is the missing number?

OK, the answer is 6, right? Because we know that 6 – 2 = 4.  

Now that we are at a higher level, we do not use blank boxes. It is uncool. Instead, we use a letter (usually an x or y, but any letter is fine).

So we would write:

It is really that simple. The letter (in this case an x) just means "we don't know this yet", and is often called the unknown or the variable.

And when you solve it you write:

Why Use a Letter?

	Because:
	it is easier to write "x" than drawing empty boxes (and easier to say "x" than "the empty box")
	if there were several empty boxes (several "unknowns") we can use a different letter for each one.

How to Solve

Algebra is just like a puzzle where you start with something like "x-2 = 4" and you want to end up with something like "x = 6".

But instead of saying "obviously x=6", we use this neat step-by-step approach:

• Work out what do we need to remove to get "x = ..."
• Remove it by doing the opposite (adding is the opposite of subtracting)
• Do that to both sides

Here is an example:

Why did we add 2 to both sides?

To "keep the balance"...

Just remember this: