posted by Lea .
Simplify (x-7)( x+7)
You can multiply these binomials like any other.
x times x and x times 7
then -7 times x and - 7 times 7
x^2 + 7x - 7x -49
Or you can recognize this pair as a sum and difference which always multiplies to be the difference of two squares.
(a+b)(a-b) = a^2 -b^2