An equation says two things are equal. The equals sign is a balance: whatever sits on the left weighs exactly the same as whatever sits on the right. Solving for x means getting it alone on one side — without ever tipping that balance.

The trick is the inverse operation: to undo something, do its opposite. And to keep the balance level, you must do it to both sides. Take:

Here 5 was added to x, so we undo it by subtracting 5 from both sides. The left becomes x on its own; the right becomes 7:

Multiplication works the same way with its inverse, division. In 3x = 12, the x is multiplied by 3, so we divide both sides by 3:

Everything here rests on knowing what x stands for — substituting a value back in is how you check your answer. The inverses themselves are just division and subtraction used to peel away whatever surrounds the unknown.

See it balanced

Picture the equation as a pair of scales. Subtracting 5 from one pan would tip it — so we take 5 off both pans at once, leaving x alone and the scales still level. Step through it.

See it explained

Sal Khan solves one-step equations by adding or subtracting the same thing from both sides.