Factorise 18x 9

Factorising 18x + 9: A Comprehensive Guide

This article provides a thorough explanation of how to factorise the algebraic expression 18x + 9. We will explore the concept of factorization, detail the steps involved in this specific example, and delve into the underlying mathematical principles. This guide is suitable for students learning algebra, and aims to build a strong foundational understanding of this crucial mathematical skill. We'll also address frequently asked questions and offer further examples to solidify your understanding.

Understanding Factorisation

Factorisation, in its simplest form, is the process of breaking down a mathematical expression into smaller, simpler components, called factors, that when multiplied together, give the original expression. Think of it like reverse multiplication. Just as we can multiply numbers to get a product, factorisation allows us to find the numbers (or expressions) that, when multiplied, produce a given expression. This is a fundamental skill in algebra, used extensively in solving equations, simplifying expressions, and understanding the relationships between variables.

Step-by-Step Factorisation of 18x + 9

The expression we're working with is 18x + 9. To factorise it, we need to find the greatest common factor (GCF) of the two terms, 18x and 9.

1. Find the Greatest Common Factor (GCF):

First, let's identify the factors of each term:

• Factors of 18x: 1, 2, 3, 6, 9, 18, x, 2x, 3x, 6x, 9x, 18x
• Factors of 9: 1, 3, 9

The greatest common factor of 18x and 9 is 9. Both 18x and 9 are divisible by 9.

2. Factor out the GCF:

Now that we've found the GCF, we can factor it out from the original expression:

18x + 9 = 9(2x + 1)

This means that 9 multiplied by (2x + 1) equals 18x + 9. We've successfully factorised the expression!

Verification: Expanding the Factorised Form

To ensure our factorisation is correct, we can expand the factorised form:

9(2x + 1) = 9 * 2x + 9 * 1 = 18x + 9

This confirms that our factorisation is accurate, as expanding the factorised form gives us the original expression.

The Importance of the Greatest Common Factor

It's crucial to always find the greatest common factor. If we had only factored out a common factor of 3, we would have obtained:

3(6x + 3)

While this is technically a factorised form, it's not fully factorised because the expression within the parenthesis can still be further simplified. The expression (6x + 3) also has a common factor of 3, which we can then factor out again, resulting in:

3 * 3(2x + 1) = 9(2x + 1)

This demonstrates why finding the greatest common factor from the outset is the most efficient and accurate method.

Expanding on Factorisation Techniques

The method used above, factoring out the GCF, is a fundamental technique. However, more complex expressions require additional strategies. Let's briefly explore some of them:

• Difference of Squares: This technique applies to expressions of the form a² - b², which factorises to (a + b)(a - b). For example, x² - 9 = (x + 3)(x - 3).

• Quadratic Trinomials: Expressions of the form ax² + bx + c can be factorised using various methods, such as the quadratic formula, completing the square, or factoring by grouping. For example, x² + 5x + 6 = (x + 2)(x + 3).

• Grouping: This method is helpful for expressions with four or more terms. We group terms with common factors and then factor out the common factors from each group. For example, 2xy + 2x + 3y + 3 = 2x(y + 1) + 3(y + 1) = (2x + 3)(y + 1)

Further Examples of Factorisation

Let's practice with a few more examples to reinforce our understanding:

• Factorise 15y - 20: The GCF is 5. Therefore, 15y - 20 = 5(3y - 4)

• Factorise 2x² + 4x: The GCF is 2x. Therefore, 2x² + 4x = 2x(x + 2)

• Factorise 6a²b + 9ab²: The GCF is 3ab. Therefore, 6a²b + 9ab² = 3ab(2a + 3b)

The Significance of Factorisation in Algebra

Factorisation is not just a standalone skill; it's a critical tool in various algebraic manipulations. Its applications include:

• Solving Equations: Factorisation is essential for solving quadratic and higher-degree equations. By setting the factorised expression equal to zero, we can find the roots or solutions of the equation.

• Simplifying Expressions: Factorisation helps simplify complex algebraic expressions, making them easier to work with and understand.

• Graphing Functions: The factorised form of a quadratic expression reveals the x-intercepts of its graph (parabola).

• Calculus: Factorisation plays a crucial role in differentiation and integration.

Frequently Asked Questions (FAQ)

Q1: What happens if I don't find the greatest common factor?

A1: If you don't find the greatest common factor, you will have a partially factorised expression. You will need to perform further factorisation steps to fully simplify the expression, as illustrated in the example with factoring out only 3 initially from 18x+9.

Q2: Can any algebraic expression be factorised?

A2: No. Some algebraic expressions cannot be factorised using standard methods. These expressions are considered prime or irreducible.

Q3: Are there different methods for factorisation?

A3: Yes, various methods exist, depending on the complexity of the expression. The GCF method is fundamental, but other techniques like difference of squares, quadratic trinomial factoring, and grouping are used for more complex expressions.

Q4: Why is factorisation important?

A4: Factorisation simplifies algebraic expressions, making them easier to manipulate and solve equations. It's a cornerstone skill in algebra and has applications across numerous mathematical disciplines.

Conclusion

Factorising algebraic expressions, as demonstrated through the example of 18x + 9, is a fundamental skill in algebra. By understanding the concept of the greatest common factor (GCF) and applying the appropriate techniques, we can effectively simplify expressions and solve equations. The ability to factorise efficiently is essential for success in higher-level mathematics. Remember to always check your work by expanding the factorised form to verify its equivalence to the original expression. Through consistent practice and application, factorisation will become a second-nature tool in your mathematical arsenal. Remember to explore the various methods and practice regularly to build confidence and proficiency. Mastering factorisation will significantly enhance your understanding and abilities in algebra and beyond.