Exercise 63 Page 62

Let's write the difference of squares pattern. a^2- b^2 = ( a+ b)( a- b)Notice that the left-hand side has no middle term with a variable. To see why that happens, let's expand the product on the right-hand side by using the F O I L method.

As we can see, the outer and the inner terms are opposite of each other. Then, when these terms are added together the sum is zero. ( a+ b)( a- b) &= a^2 - a b + a b - b^2 &= a^2- b^2