Skyrocket Quadratic Trinomial Skills: Killer Easy Tips 8

Factorising Non-Monic Quadratic Trinomials Mixed Signs

Factorising Non-Monic Quadratic Trinomials: Mixed Signs

As a high school student, mastering the art of factorising quadratic trinomials with mixed signs is crucial for your success in mathematics. Non-monic quadratic trinomials with mixed signs are expressions in the form $ax^2 + bx + c$, where $a$, $b$, and $c$ are constants, $a \neq 0$, and the signs of $b$ and $c$ are different. With these killer easy tips, you’ll be able to skyrocket your quadratic trinomial factoring skills in no time!

Understand the Goal of Factorising

Before diving into the tips and techniques, it’s essential to understand the goal of factorising quadratic trinomials. Factorising means rewriting the quadratic trinomial as a product of two linear factors. In other words, we want to find two numbers $p$ and $q$ such that:

$ax^2 + bx + c = (px + q)(rx + s)$

Where $pr = a$, $ps + qr = b$, and $qs = c$.

Understanding this goal will help you approach factorising with clarity and purpose.

Killer Tip #1: Identify the Coefficients and Constant Term

To begin factorising a non-monic quadratic trinomial with mixed signs, identify the coefficients $a$, $b$, and the constant term $c$. These values will be your guiding light throughout the factoring process. Let’s consider an example:

$3x^2 – 11x – 4$

In this case, $a = 3$, $b = -11$, and $c = -4$.


$3x^2 – 11x – 4$ $a = 3$, $b = -11$, $c = -4$

Killer Tip #2: Find the Product of $a$ and $c$

To factor a non-monic quadratic trinomial with mixed signs, you need to find the product of the coefficient $a$ and the constant term $c$. In our example, we calculate:

$ac = 3 \times (-4) = -12$

This product will help you determine the possible factor pairs in the next step.


$3x^2 – 11x – 4$ $ac = 3 \times (-4) = -12$

Killer Tip #3: Find Factor Pairs of $ac$

Now, find the factor pairs of the product $ac$. Factor pairs are two numbers that, when multiplied together, give the product $ac$. In our example, the factor pairs of $-12$ are:

$1$ and $-12$ $-1$ and $12$ $2$ and $-6$ $-2$ and $6$ $3$ and $-4$ $-3$ and $4$


$3x^2 – 11x – 4$ $ac = -12$ Factor pairs of $-12$: $(1, -12)$, $(-1, 12)$, $(2, -6)$, $(-2, 6)$, $(3, -4)$, $(-3, 4)$

Killer Tip #4: Identify the Correct Factor Pair

Among the factor pairs, identify the pair whose sum equals the coefficient of $x$ ($b$). In our example, we need to find the factor pair that adds up to $-11$. Let’s check each pair:

$1 – 12 = -11$ (equal to $-11$) $-1 + 12 = 11$ (not equal to $-11$) $2 – 6 = -4$ (not equal to $-11$) $-2 + 6 = 4$ (not equal to $-11$) $3 – 4 = -1$ (not equal to $-11$) $-3 + 4 = 1$ (not equal to $-11$)

Therefore, the correct factor pair is $(1, -12)$.


$3x^2 – 11x – 4$ Factor pairs of $-12$: $(1, -12)$, $(-1, 12)$, $(2, -6)$, $(-2, 6)$, $(3, -4)$, $(-3, 4)$ $1 – 12 = -11$ (matches the coefficient of $x$)

Killer Tip #5: Determine the Signs of the Factors

To determine the signs of the factors in the factored form, consider the signs of $b$ and $c$. If $b$ and $c$ have different signs, the factors will have different signs. The factor with the larger absolute value will have the same sign as $b$.

In our example, $b$ is negative, and $c$ is negative. The factor pair $(1, -12)$ has different signs, and $-12$ has the same sign as $b$ (negative).


$3x^2 – 11x – 4$ $b = -11$ (negative), $c = -4$ (negative) Factors will have different signs, and the larger factor ($-12$) will be negative

Killer Tip #6: Write the Factored Form

Now that you have identified the correct factor pair and their signs, you can write the factored form of the non-monic quadratic trinomial with mixed signs. Using the factor pair $(p, q)$ and the coefficient $a$, the factored form is:

$a(x + \frac{p}{a})(x – \frac{q}{a})$

In our example, the factored form is:

$3(x + \frac{1}{3})(x – \frac{12}{3})$

Simplify the fractions to obtain the final factored form:

$3(x + \frac{1}{3})(x – 4)$


$3x^2 – 11x – 4 = 3(x + \frac{1}{3})(x – 4)$

Practice Makes Perfect

To reinforce your understanding and build your factoring skills, practice factorising non-monic quadratic trinomials with mixed signs regularly. Start with simple examples and gradually progress to more challenging ones. Remember, the more you practice, the more confident and proficient you’ll become in factoring quadratic trinomials.

Examples to Practice:

  1. $2x^2 – 7x – 4$
  2. $3x^2 + 5x – 2$
  3. $4x^2 – 3x – 1$
  4. $5x^2 + 2x – 3$
  5. $6x^2 – 5x – 6$

Troubleshooting Common Mistakes

As you practice factorising non-monic quadratic trinomials with mixed signs, be aware of common mistakes students often make:

  1. Forgetting to consider negative factor pairs: Remember that factor pairs can be positive or negative. For example, $-1$ and $12$ are also factor pairs of $-12$.
  2. Incorrectly adding or multiplying factor pairs: Double-check your calculations when determining the sum and product of factor pairs.
  3. Mixing up the order of factors: The order of the factors does not matter, as multiplication is commutative. However, be consistent in your approach to avoid confusion.
  4. Overlooking the signs of factors: Pay attention to the signs of $b$ and $c$ to determine the signs of the factors in the factored form.

By being mindful of these common mistakes, you can avoid pitfalls and strengthen your factoring skills.


Factorising non-monic quadratic trinomials with mixed signs may seem daunting at first, but with these killer easy tips, you’ll be able to master this essential skill in no time. Remember to identify the coefficients and constant term, find the product of $a$ and $c$, find factor pairs of $ac$, identify the correct factor pair, determine the signs of the factors, and write the factored form. Practice regularly, start with simple examples, and gradually challenge yourself with more complex trinomials.

As you gain confidence in factoring non-monic quadratic trinomials with mixed signs, you’ll be well-prepared to tackle more advanced topics in algebra and beyond. Keep honing your skills, and don’t hesitate to seek help from your teachers or tutors if you encounter difficulties along the way. With dedication and practice, you’ll become a quadratic trinomial factoring pro in no time!

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