Answer:
WHEN THE SUM of two numbers multiplies their difference --
(a + b)(a − b)
-- then the product is the difference of their squares:
(a + b)(a − b) = a2 − b2
For, the like terms will cancel.
Symmetrically, the difference of two squares can be factored:
x2 − 25 = (x + 5)(x − 5)
x2 is the square of x. 25 is the square of 5.
The sum of two squares -- a2 + b2 -- cannot be factored. See Section 2.
Example 1. Multiply (x3 + 2)(x3 − 2).
Solution. Recognize the form:
(a + b)(a − b)
The product will be the difference of two squares:
(x3 + 2)(x3 − 2) = x6 − 4.
x6 is the square of x3. 4 is the square of 2.
Upon seeing the form (a + b)(a − b), the student should not do the FOIL method. The student should recognize immediately that the product will be a2 − b2.
That is skill in algebra.
And the order of factors never matters:
(a + b)(a − b) = (a − b)(a + b) = a2 − b2.
