Non-Monic Difference of Squares Factorising Made Simple

Factorising Difference of Squares Non-Monic Coefficients

Factorising is an essential skill in algebra that allows you to break down complex expressions into simpler, more manageable terms. One of the most important factorising techniques is the difference of squares, which is used to factorise expressions in the form of \(a^2-b^2\). However, when dealing with non-monic coefficients, such as \(4x^2-9y^2\), many students find themselves struggling. In this article, we’ll explore the concept of non-monic difference of squares and provide you with simple steps to master this crucial factorising skill.

Understanding the Difference of Squares

Before diving into non-monic difference of squares, let’s review the basic concept of the difference of squares. The difference of squares formula states that:

\(a^2-b^2 = (a+b)(a-b)\)

This means that when you have an expression in the form of \(a^2-b^2\), you can factorise it into \((a+b)(a-b)\).

For example, let’s factorise \(x^2-9\):

\(x^2-9 = (x+3)(x-3)\)

By applying the difference of squares formula, we can easily factorise the expression.

Non-Monic Difference of Squares

Non-monic difference of squares are expressions in the form of \(a^2x^2-b^2y^2\), where \(a\) and \(b\) are non-monic coefficients (i.e., not equal to 1). These expressions can be factorised using a similar approach to the standard difference of squares formula, with a few additional steps.

Factorising Non-Monic Difference of Squares

To factorise non-monic difference of squares, follow these simple steps:

Step 1: Identify the terms \(a^2x^2\) and \(b^2y^2\).

Step 2: Find the square roots of \(a^2\) and \(b^2\):

\(\sqrt{a^2} = a\)
\(\sqrt{b^2} = b\)

Step 3: Factorise the expression using the difference of squares formula, treating \(ax\) and \(by\) as single terms:

\(a^2x^2-b^2y^2 = (ax+by)(ax-by)\)

Step 4: Expand the factored terms if required.

Let’s apply these steps to factorise \(4x^2-9y^2\):

Step 1: \(a^2x^2 = 4x^2\) and \(b^2y^2 = 9y^2\)

Step 2: \(\sqrt{4} = 2\) and \(\sqrt{9} = 3\)

Step 3: \(4x^2-9y^2 = (2x+3y)(2x-3y)\)

Step 4: No expansion required.

Therefore, \(4x^2-9y^2 = (2x+3y)(2x-3y)\).

Factorising Non-Monic Difference of Squares with Negative Coefficients

When dealing with negative coefficients, the process remains the same, but you need to be careful with the signs when factorising.

For example, let’s factorise \(9x^2-16y^2\):

Step 1: \(a^2x^2 = 9x^2\) and \(b^2y^2 = 16y^2\)

Step 2: \(\sqrt{9} = 3\) and \(\sqrt{16} = 4\)

Step 3: \(9x^2-16y^2 = (3x+4y)(3x-4y)\)

Step 4: No expansion required.

Therefore, \(9x^2-16y^2 = (3x+4y)(3x-4y)\).

Practice Makes Perfect

Factorising non-monic difference of squares may seem challenging at first, but with practice, you’ll soon find yourself mastering this technique. Start by identifying the non-monic coefficients and the terms \(a^2x^2\) and \(b^2y^2\), then follow the steps to factorise the expression.

As you practice, you’ll develop a deeper understanding of the patterns and relationships between the terms, making it easier to recognise and factorise non-monic difference of squares quickly.

Common Mistakes to Avoid

When factorising non-monic difference of squares, there are a few common mistakes to watch out for:

  1. Forgetting to find the square roots of \(a^2\) and \(b^2\): Make sure to take the square roots of the non-monic coefficients before factorising.
  2. Incorrectly treating \(ax\) and \(by\) as separate terms: Remember to treat \(ax\) and \(by\) as single terms when applying the difference of squares formula.
  3. Mishandling negative coefficients: Pay attention to the signs of the coefficients and ensure that you factor them correctly.

By being aware of these common pitfalls and double-checking your work, you can avoid mistakes and master non-monic difference of squares factorising.

Applying Non-Monic Difference of Squares in Problem Solving

Factorising non-monic difference of squares is not only an essential skill in algebra but also has practical applications in problem-solving. By breaking down complex expressions into simpler, factored forms, you can often find solutions to equations, inequalities, and other mathematical problems more easily.

For example, consider the equation \(4x^2-9y^2 = 0\). By factorising the left-hand side using the non-monic difference of squares technique, we get:

\((2x+3y)(2x-3y) = 0\)

From this factored form, we can easily see that the solutions to the equation are \(2x+3y = 0\) or \(2x-3y = 0\), which can be solved further to find the values of \(x\) and \(y\).


Factorising non-monic difference of squares is a crucial skill for anyone studying algebra. By understanding the basic concept of the difference of squares and learning how to adapt the formula for non-monic coefficients, you can easily factorise even the most complex expressions.

Remember to practice regularly, follow the step-by-step process, and be aware of common mistakes. With time and dedication, you’ll find yourself factorising non-monic difference of squares with confidence, opening up new possibilities for problem-solving and mathematical exploration.

Unlock your full learning potential—download our expertly crafted slide files for free and transform your self-study sessions!

Discover more enlightening videos by visiting our YouTube channel!


Algebra Algebraic Fractions Arc Binomial Expansion Capacity Common Difference Common Ratio Differentiation Double-Angle Formula Equation Exponent Exponential Function Factorise Functions Geometric Sequence Geometric Series Index Laws Inequality Integration Kinematics Length Conversion Logarithm Logarithmic Functions Mass Conversion Mathematical Induction Measurement Perfect Square Perimeter Prime Factorisation Probability Product Rule Proof Pythagoras Theorem Quadratic Quadratic Factorise Ratio Rational Functions Sequence Sketching Graphs Surds Time Transformation Trigonometric Functions Trigonometric Properties Volume

Related Articles


Your email address will not be published. Required fields are marked *