Study Guides/Maths/a^3 + b^3 + c^3 Formula
Study Guide · Maths

Algebraic Formula for a³ + b³ + c³

In algebra, polynomials and identities are crucial for solving complex equations quickly. One of the most important and frequently tested polynomial identities in mathematics is the formula involving the sum of three cubes: $a^3 + b^3 + c^3$.

Question (Click to Flip)

What is the value of x^3 + y^3 + z^3 if x+y+z = 0?

Answer

According to the conditional identity, if x + y + z = 0, then x^3 + y^3 + z^3 equals exactly 3xyz.

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Key Facts

This identity is widely used in competitive exams like JEE, SSC, and SAT.

Always check if a + b + c = 0 first, as it simplifies the problem instantly.

The formula helps in factoring large polynomials.

1. The Standard Identity Formula

The complete algebraic identity is written as:

  • $a^3 + b^3 + c^3 - 3abc = (a + b + c)(a^2 + b^2 + c^2 - ab - bc - ca)$

To isolate $a^3 + b^3 + c^3$, you move $3abc$ to the right side:

  • $a^3 + b^3 + c^3 = (a + b + c)(a^2 + b^2 + c^2 - ab - bc - ca) + 3abc$

2. The Special Condition (When a + b + c = 0)

There is a very important special case for this formula. If the sum of the three variables is zero ($a + b + c = 0$), then the entire right side of the equation before the $+ 3abc$ becomes zero (because zero multiplied by anything is zero).

  • Therefore, if $a + b + c = 0$, then $a^3 + b^3 + c^3 = 3abc$.

Questions and Answers

What is the value of x^3 + y^3 + z^3 if x+y+z = 0?+

According to the conditional identity, if x + y + z = 0, then x^3 + y^3 + z^3 equals exactly 3xyz.

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