Polynomial Factoring Calculator

What Is Polynomial Factoring?

Polynomial factoring is the process of rewriting a polynomial as a product of two or more simpler polynomials. It is the algebraic inverse of expanding or multiplying polynomials. For example, x² − 9 factors into (x + 3)(x − 3), because multiplying those two binomials gives back x² − 9. Factoring is one of the most important skills in algebra and forms the foundation for solving polynomial equations, simplifying rational expressions, finding roots, and working with polynomials in calculus.

Why Factor Polynomials?

• Solving equations: Setting each factor equal to zero gives the roots instantly. If p(x) = (x−3)(x+2), then x = 3 and x = −2.
• Simplifying rational expressions: Common polynomial factors in a fraction's numerator and denominator can be cancelled.
• Finding x-intercepts: The real roots of a polynomial are its x-intercepts on a graph.
• Calculus applications: Partial fraction decomposition requires factored denominators. Limits, derivatives, and integrals are often simplified by factoring.
• Understanding multiplicity: Repeated factors like (x−2)² indicate the root x = 2 has multiplicity 2, meaning the graph touches but does not cross the x-axis there.

The 8 Factoring Techniques

1. Greatest Common Factor (GCF)

Always try to factor out the GCF first. The GCF is the largest monomial that divides every term. Example: 6x³ + 9x² = 3x²(2x + 3). The GCF here is 3x². This step reduces the degree of the remaining polynomial and simplifies all further factoring.

2. Difference of Squares

Any binomial of the form a² − b² factors as (a + b)(a − b). Both terms must be perfect squares, and the sign between them must be minus. Example: 4x² − 25 = (2x)² − 5² = (2x + 5)(2x − 5). Note that a sum of squares a² + b² does not factor over the real numbers.

3. Perfect Square Trinomial

A trinomial a² + 2ab + b² factors as (a + b)², and a² − 2ab + b² factors as (a − b)². Example: x² + 6x + 9 = (x + 3)². To check: the first and last terms must be perfect squares, and the middle term must equal twice their product.

4. Sum of Cubes

a³ + b³ = (a + b)(a² − ab + b²). Remember SOAP: Same, Opposite, Always Positive for the signs. Example: x³ + 27 = x³ + 3³ = (x + 3)(x² − 3x + 9). The trinomial factor is always irreducible over the reals.

5. Difference of Cubes

a³ − b³ = (a − b)(a² + ab + b²). Example: x³ − 8 = x³ − 2³ = (x − 2)(x² + 2x + 4). The signs: first factor has minus, trinomial starts positive, all remaining signs positive.

6. Quadratic Trinomial (Quadratic Formula)

For any quadratic ax² + bx + c, the discriminant is Δ = b² − 4ac. If Δ ≥ 0, real roots exist: r = (−b ± √Δ) / (2a), and the polynomial factors as a(x − r₁)(x − r₂). If Δ < 0, the quadratic is irreducible over the reals.

7. Factoring by Grouping

This technique applies to 4-term polynomials. Group into two pairs, factor the GCF from each pair, then extract the common binomial. Example: 2x³ + 6x² − 2x − 6 = (2x³ + 6x²) + (−2x − 6) = 2x²(x + 3) − 2(x + 3) = (2x² − 2)(x + 3) = 2(x² − 1)(x + 3) = 2(x + 1)(x − 1)(x + 3).

8. Rational Root Theorem and Synthetic Division

For degree 3 and higher, the Rational Root Theorem lists all possible rational roots as ±p/q, where p divides the constant term and q divides the leading coefficient. Each candidate is tested; if p(r) = 0, then (x − r) is a factor. Synthetic division then reduces the polynomial degree by one, and the process repeats until completely factored.

Reference Table: Common Factored Forms

Form	Factored Form	Example
a²−b²	(a+b)(a−b)	x²−9 = (x+3)(x−3)
a²+2ab+b²	(a+b)²	x²+6x+9 = (x+3)²
a³+b³	(a+b)(a²−ab+b²)	x³+8 = (x+2)(x²−2x+4)
a³−b³	(a−b)(a²+ab+b²)	x³−27 = (x−3)(x²+3x+9)
a⁴−b⁴	(a²+b²)(a+b)(a−b)	x⁴−16 = (x²+4)(x+2)(x−2)