Alaa,

The expansion follows the distributive laws which say

a(b + c) = ab + ab and (b + c)a = ba + ca.

I am going to expand and simplify a similar expression, (x + 5)(x - 3).

I want to see this as a(b + c) where a = (x + 5), b = x and c = -3. The first distributive law then gives me

(x + 5)(x - 3) = (x + 5)x + (x + 5)(-3).

Using the second form of the distributive law on the two terms on the right side of the equation above gives

(x + 5)(x - 3) = (x + 5)x + (x + 5)(-3)
= x² + 5x + (-3)x + 5(-3) = x² + 5x -3x - 15.

Finally I can simplify this using the fact that 5x - 3x = 2x so I get

(x + 5)(x - 3) = x² + 2x - 15.

Now try (x - 9)(x + 2),
Penny