x^3 + y^3 = (x + y)^3 - 3xy(x + y) = 10^3 - 3 \cdot 21 \cdot 10 = 1000 - 630 = 370 - Treasure Valley Movers

Understanding the Identity: x³ + y³ = (x + y)³ − 3xy(x + y) Applied to a Numerical Proof

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Unlocking the Power of Algebraic Identities: A Deep Dive into x³ + y³ = (x + y)³ − 3xy(x + y)

Mathematics is filled with elegant identities that simplify complex expressions and reveal hidden patterns. One such powerful identity is:

x³ + y³ = (x + y)³ − 3xy(x + y)

This formula is not only foundational in algebra but also incredibly useful for solving equations involving cubes — especially when numerical substitutions are involved.

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What is the Identity?

The identity
x³ + y³ = (x + y)³ − 3xy(x + y)
expresses the sum of two cubes in terms of a binomial cube minus a product-dependent correction term. This identity allows us to expand and simplify cubic expressions efficiently, particularly when factoring or evaluating expressions numerically.

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Breaking Down the Formula

Start with the right-hand side:

1. Expand (x + y)³ using the binomial theorem:
   (x + y)³ = x³ + y³ + 3xy(x + y)

2. Rearranging to isolate x³ + y³, we get:
   x³ + y³ = (x + y)³ − 3xy(x + y)

This equation forms the basis for simplifying expressions involving cubes without direct expansion.

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A Practical Numerical Illustration

Let’s apply this identity to a concrete example:

Given:
x = 10, y = 21

Our goal:
Evaluate the expression x³ + y³ using the identity
x³ + y³ = (x + y)³ − 3xy(x + y), then verify it equals 370.

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Step 1: Plug in the values