Problem 42 - Algebra 2

Question

Expand each binomial. $$ (x+5 y)^{3} $$

Step-by-Step Solution

Answer

The expansion of \((x+5y)^3\) is \(x^3 + 15x^2y + 75xy^2 + 125y^3\).

Step 1: Identify the Components

From the binomial expression, two components can be identified, which are x and 5y. Also, note the exponent 3.

Step 2: Apply the Binomial Theorem

According to the Binomial Theorem, the expansion of \((a+b)^n\) where a and b are any real numbers, and n is a natural number, is given as \((a+b)^n = \sum_{r=0}^{n} {n \choose r} a^{n-r}b^r\). Here, \(a = x\), \(b = 5y\), and \(n = 3\).

Step 3: Expand

Applying the Binomial Theorem to expand the expression results in \((x+5y)^3 = {3 \choose 0} x^{3} (5y)^{0} + {3 \choose 1} x^{2} (5y)^{1} + {3 \choose 2} x^{1} (5y)^{2} + {3 \choose 3} x^{0} (5y)^{3}\). Simplify the binomial coefficients and expressions resulting in \(x^3 + 3 \cdot x^2 \cdot 5y + 3 \cdot x \cdot (5y)^2 + (5y)^3\).

Step 4: Simplify

Rewrite the expression as \(x^3 + 15x^2y + 75xy^2 + 125y^3\)

Key Concepts

Binomial Theorem

The Binomial Theorem is a fundamental principle in algebra that provides a method to expand expressions of the form \((a+b)^n\) into a sum of terms involving powers of \(a\) and \(b\). This theorem is immensely powerful and simplifies the process of raising a binomial to any given power. Using the expression from our exercise, \((x+5y)^3\), the theorem informs us of how to distribute the powers across both components \(x\) and \(5y\).
The expansion is determined by the formula:

1. \((a+b)^n = \sum_{r=0}^{n} {n \choose r} a^{n-r}b^r\) where \({n \choose r}\) are binomial coefficients.

This formula breaks down the expansion into specific terms that add up after computing the necessary powers and coefficients. In this case, the theorem helps convert a potentially complex power into a manageable polynomial expression.

Pascal's Triangle

Pascal's Triangle is a triangular array where each number is the sum of the two directly above it. It's a powerful tool used to find the binomial coefficients quickly and easily, which are essential components of the Binomial Theorem. In our exercise, we expanded \((x+5y)^3\), and the coefficients needed are obtained from the third row of Pascal's Triangle.
The third row in Pascal’s Triangle is:

• 1, 3, 3, 1

These numbers correspond to the coefficients \({3 \choose 0}, {3 \choose 1}, {3 \choose 2}, {3 \choose 3}\) respectively, and tell us how many ways each power can be formed in the expanded polynomial. Pascal’s Triangle simplifies generating these coefficients without complex calculations and helps reinforce the relationships between terms in the expansion.

Polynomial Expansion

Polynomial Expansion involves expressing a binomial raised to a certain power as a sum of polynomial terms. This transformation is seen in exercises like the one provided:\((x+5y)^3\). Using the Binomial Theorem and Pascal's Triangle, this binomial becomes:

• \(x^3 + 3x^2(5y) + 3x(5y)^2 + (5y)^3\)

Breaking this down:

• Start with \(x^3\), which is simply \(x\) raised to the power of 3.
• The term \(3x^2(5y)\) signifies multiplying \(x^2\) by \(5y\) with the coefficient 3.
• Next, \(3x(5y)^2\) involves raising \(5y\) to the power of 2 and then multiplying with \(x\) and the coefficient of 3.
• Finally, \((5y)^3\) is \(5y\) raised to the power of 3.

The polynomial expansion turns these calculations into parts of a comprehensive expression, illustrating the systematic distribution of powers and coefficients.

Algebraic Expressions

Algebraic expressions are mathematical phrases that can contain numbers, variables, and operation signs. In this exercise, \((x+5y)^3\), we're working with a binomial expression composed of variables \(x\) and \(y\), and a constant 5. Such expressions quantitatively represent relationships between different elements using algebra.
The simplified form is given as:

• \(x^3 + 15x^2y + 75xy^2 + 125y^3\)

Here each term in the expression signifies different combinations of the powers of \(x\) and \(y\), demonstrating how different elements combine algebraically. Each term is a product of a coefficient, powers of \(x\), and powers of \(y\). Understanding these components and their interactions in algebraic expressions is key to mastering higher-level algebra and using algebraic principles effectively.