Question

Write the three special product factoring patterns. Give an example of each pattern.

Short answer

The three special product factoring patterns are: Difference of Squares: \( a^2 - b^2 = (a+b)(a-b) \) example: \( 9x^2 - 16 = (3x+4)(3x-4) \); Perfect Square Trinomial: \( a^2 + 2ab + b^2 = (a+b)^2 \) and \( a^2 - 2ab + b^2 = (a-b)^2 \) example: \( 4x^2 + 12x + 9 = (2x+3)^2 \) and \( 4x^2 - 12x + 9 = (2x-3)^2 \); Difference or Sum of Cubes: \( a^3 - b^3 = (a-b)(a^2+ab+b^2) \) and \( a^3 + b^3 = (a+b)(a^2-ab+b^2) \) example: \( 8x^3 - 27 = (2x-3)(4x^2+6x+9) \) and \( 8x^3 + 27 = (2x+3)(4x^2-6x+9) \).

Step-by-step solution

Difference of Squares

The formula for the Difference of Squares is: \( a^2 - b^2 = (a+b)(a-b) \). For example, \( 9x^2 - 16 = (3x+4)(3x-4) \). In this expression, \( a = 3x \) and \( b = 4 \).

Perfect Square Trinomial

The formula for the Perfect Square Trinomial is: \( a^2 + 2ab + b^2 = (a+b)^2 \) or \( a^2 - 2ab + b^2 = (a-b)^2 \). For positive, \( 4x^2 + 12x + 9 = (2x+3)^2 \). Here, \( a = 2x \) and \( b = 3 \). For negative, \( 4x^2 - 12x + 9 = (2x-3)^2 \). Here, \( a = 2x \) and \( b = 3 \).

Difference or Sum of Cubes

The formula for the Difference of Cubes is: \( a^3 - b^3 = (a-b)(a^2+ab+b^2) \). And for the Sum of Cubes: \( a^3 + b^3 = (a+b)(a^2-ab+b^2) \). For example, in difference: \( 8x^3 - 27 = (2x-3)(4x^2+6x+9) \). Here, \( a =2x \) and \( b = 3 \). In sum: \( 8x^3 + 27 = (2x+3)(4x^2-6x+9) \). Here, \( a = 2x \) and \( b = 3 \).

Key concepts

Difference of Squares

The difference of squares is a pattern used in algebra to simplify expressions that subtract one square number from another. Learning this factoring technique is quite straightforward once you recognize the pattern, which looks like this: \( a^2 - b^2 \). This expression can be broken down into two factors \( (a+b)(a-b) \).

Why does this work? Think of it as taking two perfect squares and realizing that their difference will always factor into the product of the sum and difference of their square roots. As shown in the step-by-step solution, for \( 9x^2 - 16 \), which is the difference between the squares of \(3x\) and \(4\), the factorization is \( (3x+4)(3x-4) \).

Here's a handy tip: Whenever you come across a quadratic expression where both terms are perfect squares separated by a minus sign, you can quickly apply this pattern to factor it into two binomials.

Perfect Square Trinomial

A perfect square trinomial looks quite different at first glance, but it's another common pattern in factoring. It comes from squaring a binomial, either \( (a+b)^2 \) or \( (a-b)^2 \), and results in a trinomial of the form \( a^2 + 2ab + b^2 \) or \( a^2 - 2ab + b^2 \), respectively.

The key indicators of a perfect square trinomial include the first and last terms being perfect squares, and the middle term being twice the product of the square roots of these terms. Take for example \( 4x^2 + 12x + 9 \), where the first term, \( 4x^2 \), comes from \( (2x)^2 \), and the last term, \( 9 \), from \( 3^2 \). The middle term, \( 12x \), is exactly twice the product of \( 2x \) and \( 3 \). Thus, it factors neatly into \( (2x+3)^2 \).

If you're dealing with a trinomial where the sign in the middle is negative, as in \( 4x^2 - 12x + 9 \), the signs in the binomial factor will be negative as well—\( (2x-3)^2 \). Remember, for a perfect square, the middle term is key: its coefficient must be double the product of the two square roots.

Sum of Cubes

Moving on from squares to cubes, another remarkable pattern involves the sum of cubes. Just like with the difference of squares, sums and differences of cubes have specific factoring formulas. The sum of cubes formula is \( a^3 + b^3 = (a+b)(a^2-ab+b^2) \).

The conceptual leap here is to understand that when you add two cube numbers, their sum can be broken down into a binomial and a trinomial. Considering our example, \( 8x^3 + 27 \), you can view \( 8x^3 \) as \( (2x)^3 \) and \( 27 \) as \( 3^3 \). Using the sum of cubes formula, this factors into \( (2x+3)(4x^2-6x+9) \).

This pattern can be less intuitive than the difference of squares, so it helps to memorize the formula and practice applying it to different sums of cube expressions.

Difference of Cubes

On the other side of the cube world is the difference of cubes pattern. This one applies when you subtract one cube number from another, and it is factored using the formula \( a^3 - b^3 = (a-b)(a^2+ab+b^2) \).

Similar to the sum of cubes, but with a notable difference in signs, this pattern can be applied to expressions like \( 8x^3 - 27 \), representing the difference between \( (2x)^3 \) and \( 3^3 \). Factoring according to our pattern yields \( (2x-3)(4x^2+6x+9) \).

It's helpful to look out for cube numbers and practice spotting the difference of cubes pattern in algebraic expressions, as it can save you a lot of time when you're trying to simplify or solve equations.