X 2 X 72 Factorise

Factorising x² + 72x: A Comprehensive Guide

Understanding how to factorise quadratic expressions is a fundamental skill in algebra. This article provides a comprehensive guide to factorising the expression x² + 72x, exploring various methods, explaining the underlying concepts, and addressing common questions. We'll move beyond simply finding the answer to develop a deeper understanding of the process and its applications.

Introduction: What is Factorisation?

Factorisation, in the context of algebra, is the process of breaking down a mathematical expression into simpler components—its factors—that when multiplied together, produce the original expression. Think of it like reverse multiplication. For example, factorising 12 might give you 2 x 2 x 3. Similarly, factorising a quadratic expression like x² + 72x involves finding expressions that, when multiplied, result in the original quadratic.

This particular example, x² + 72x, presents a slightly simpler scenario than many quadratic expressions because it lacks a constant term (a number without a variable). This absence simplifies the factorisation process considerably.

Method 1: Identifying the Greatest Common Factor (GCF)

The most straightforward approach to factorising x² + 72x is by identifying and extracting the Greatest Common Factor (GCF). The GCF is the largest expression that divides evenly into both terms of the quadratic.

In our case, both x² and 72x contain an 'x'. Therefore, 'x' is a common factor. We can rewrite the expression as:

x² + 72x = x(x + 72)

This is the factorised form. We've successfully broken down the original expression into two factors: x and (x + 72). If we were to expand this factored form using the distributive property (multiplying x by both terms inside the parentheses), we would get back to our original expression, x² + 72x.

Method 2: Visualising the Area Model (for beginners)

For those who find the abstract nature of algebra challenging, a visual approach can be helpful. We can represent the expression x² + 72x using an area model. Imagine a rectangle with an area represented by x² + 72x.

• One side of the rectangle can be represented by 'x'.
• To find the other side, we need to determine what, when multiplied by 'x', gives us x² + 72x. That's (x + 72).

Therefore, our rectangle has sides of length 'x' and '(x + 72)', confirming that x(x + 72) represents the area (and thus the factorisation) of x² + 72x. This area model provides a concrete visual representation of the abstract concept of factorisation.

Deeper Dive: Quadratic Expressions and their General Form

While x² + 72x is relatively simple, understanding the general form of quadratic expressions helps us tackle more complex problems. The general form of a quadratic expression is:

ax² + bx + c

where:

• 'a', 'b', and 'c' are constants (numbers).
• 'x' is the variable.

Our expression, x² + 72x, fits this general form with a = 1, b = 72, and c = 0. The fact that c = 0 simplifies the factorisation process significantly, as we don't need to find factors that add up to 'b' and multiply to 'c' (a common technique for factorising when c ≠ 0).

Comparing with More Complex Quadratic Factorisation

Let's contrast this with a more complex example: x² + 13x + 30. Here, we need to find two numbers that add up to 13 (the coefficient of x) and multiply to 30 (the constant term). Those numbers are 3 and 10. Therefore, the factorisation of x² + 13x + 30 is (x + 3)(x + 10).

The absence of the constant term ('c' = 0) in x² + 72x significantly simplifies the factorisation; we only need to find the GCF.

Applications of Factorisation: Solving Quadratic Equations

Factorisation is crucial for solving quadratic equations. A quadratic equation is an equation of the form ax² + bx + c = 0. By factorising the quadratic expression, we can find the values of 'x' that satisfy the equation.

For example, if we have the equation x² + 72x = 0, we can factorise the left side as x(x + 72) = 0. This equation is true if either x = 0 or (x + 72) = 0. Therefore, the solutions to the equation are x = 0 and x = -72.

Further Exploration: Higher-Order Polynomials

The principles of factorisation extend beyond quadratic expressions. We can factorise higher-order polynomials (expressions with terms involving x³, x⁴, and so on) using similar techniques, although they often become more complex. The GCF method, however, remains a valuable tool even with higher-order polynomials.

Frequently Asked Questions (FAQ)

Q1: Why is factorisation important?

A1: Factorisation is a fundamental skill in algebra because it allows us to simplify expressions, solve equations, and understand the structure of polynomials. It forms the basis for many advanced mathematical concepts.

Q2: Can I factorise any quadratic expression?

A2: Not all quadratic expressions can be factorised using only integers. Some require the use of more advanced techniques, such as the quadratic formula. However, the GCF method is always applicable if a common factor exists.

Q3: What if the expression had a negative coefficient for 'x'?

A3: If the expression was, for example, x² - 72x, the factorisation would be x(x - 72). The process remains the same; we still identify the GCF and factor it out.

Q4: Are there other methods for factorising quadratics?

A4: Yes, besides the GCF method and the area model, other techniques include the quadratic formula and completing the square, particularly useful when factorisation with integers is not straightforward.

Conclusion: Mastering Factorisation

Factorising x² + 72x, while seemingly simple, provides a solid foundation for understanding the broader concept of factorisation in algebra. By mastering the GCF method and understanding the underlying principles, you'll be well-equipped to tackle more complex factorisation problems and their applications in solving equations and simplifying algebraic expressions. Remember that practice is key! The more you work through examples, the more comfortable and confident you'll become with this essential algebraic skill. Don't hesitate to explore further examples and challenge yourself with more complicated quadratic expressions to deepen your understanding. The journey towards algebraic proficiency is a rewarding one, full of opportunities for intellectual growth and problem-solving satisfaction.