Step by step
The question
Question: solve 2x + 9 = 3.
We want x by itself.
Two things are stuck to x: times 2 and + 9.
First x was times 2.
Then + 9.
To take them off, we go backwards.
First we remove the + 9.
Then the times 2.
1 Remove the + 9
To remove + 9, we take away 9.
We do it on both sides.
Why both sides?
The = sign means both sides are the same amount.
If we change only one side, they are not the same any more.
+ 9 and − 9 make zero.
Cross them out.
3 − 9 = −6.
Now we have 2x = −6.
2 Remove the 2
2x means 2 times x.
We want just x.
To remove times 2, we divide by 2.
We do it on both sides, so they stay equal.
2 divided by 2 is 1.
So just x is left.
−6 divided by 2 is −3.
So x = −3!
3 Check
Let's check: put −3 in place of x.
We get 3, the same as the right side.
So x = −3 is right!
4 Type it in
The answer box takes 6 characters.
−3 has 2.
It fits.
A negative answer gets one more character, for the minus sign.
We type −3.
Let's look back.
First: remove the + 9.
Then: remove the 2.
Then: check.
Last: type it in.