# Square of a Difference

How to solve the square of a difference problems: formula, examples, and their solutions.

## Formula

(*a* - *b*)^{2} = (*a* - *b*)(*a* - *b*).

By using the FOIL method,

(*a* - *b*)(*a* - *b*) = *a*^{2} - 2*ab* + *b*^{2}.

So (*a* - *b*)^{2} = *a*^{2} - 2*ab* + *b*^{2}.

See the brown (-) signs.

The (-) sign in (*a* - *b*)^{2}

makes the middle term (-): -2*ab*.

It's the difference between

this formula and (*a* + *b*)^{2} formula.

## Example 1

Put *x*, (-), 7 into the formula.

## Example 2

Put 3*r*, (-), 2*s* into the formula.