Expanding Cubed Binomials: Box & Distribution Methods

In algebra, expanding binomials is a fundamental skill that allows you to simplify expressions and solve equations. This blog will focus on expanding cubed binomials, which involve raising a binomial to the power of 3. We’ll explore two methods: the box method and the distribution method, providing a clear understanding of each process.

Understanding Cubed Binomials

A cubed binomial is an expression in the form (a + b)³, where ‘a’ and ‘b’ can be any variable or constant. Expanding this means multiplying the binomial by itself three times.

Method 1: The Box Method

The box method is a visual and organized way to expand binomials. It involves creating a grid and multiplying terms systematically.

Steps

1. Create a 3×3 grid: Since we’re dealing with a cubed binomial (a + b)³, we need a grid with three rows and three columns.
2. Label the rows and columns: Label the rows with the terms of the first binomial (a + b) and the columns with the terms of the second binomial (a + b).
3. Multiply terms: Multiply the terms corresponding to each row and column and place the product in the intersecting box.
4. Combine like terms: Add the terms within the boxes that have the same variables and exponents.

Example

Let’s expand (x + 2)³ using the box method.

	x	2
x	x2	2x
x	x2	2x
2	2x	4

Combining like terms, we get:

x³ + 6x² + 12x + 8

Method 2: The Distribution Method

The distribution method involves using the distributive property to multiply the binomials.

Steps

1. Expand the first two binomials: Multiply (a + b) by (a + b) using the distributive property. This gives you (a² + 2ab + b²).
2. Multiply the result by the remaining binomial: Again, use the distributive property to multiply (a² + 2ab + b²) by (a + b). Distribute each term in the first expression to each term in the second expression.
3. Simplify: Combine like terms to get the final expanded form.

Example

Let’s expand (x + 2)³ using the distribution method.

1. (x + 2)(x + 2) = x² + 4x + 4
2. (x² + 4x + 4)(x + 2) = x³ + 6x² + 12x + 8

As you can see, both methods lead to the same result: x³ + 6x² + 12x + 8

Practice Questions

Here are some practice questions to solidify your understanding of expanding cubed binomials:

1. (2x + 1)³
2. (y – 3)³
3. (3a + 4b)³

Conclusion

Expanding cubed binomials can seem complex at first, but with the help of the box and distribution methods, it becomes a straightforward process. Choose the method that suits your learning style and practice regularly to master this algebraic skill. Remember, understanding binomial expansions is crucial for solving equations, simplifying expressions, and delving deeper into algebraic concepts.