Use the “sum to zero” cubes identity: If a + b + c = 8, evaluate (a − 4)^3 + (b − 3)^3 + (c − 1)^3 − 3(a − 4)(b − 3)(c − 1).

Difficulty: Easy

Correct Answer: 0

Explanation:


Introduction / Context:
This is a direct application of the identity p^3 + q^3 + r^3 − 3pqr = (p + q + r)(p^2 + q^2 + r^2 − pq − qr − rp). Whenever p + q + r = 0, the entire expression simplifies to 0. The shifts by 4, 3, and 1 are designed precisely to make the sum vanish.



Given Data / Assumptions:

  • a + b + c = 8.
  • Let p = a − 4, q = b − 3, r = c − 1.


Concept / Approach:
Compute p + q + r and use the cubes identity. If p + q + r = 0, then p^3 + q^3 + r^3 − 3pqr must be 0, regardless of the actual individual values of a, b, and c.



Step-by-Step Solution:

p + q + r = (a − 4) + (b − 3) + (c − 1) = (a + b + c) − (4 + 3 + 1) = 8 − 8 = 0Therefore, (a − 4)^3 + (b − 3)^3 + (c − 1)^3 − 3(a − 4)(b − 3)(c − 1) = 0


Verification / Alternative check:
Plug in any specific numbers satisfying a + b + c = 8, e.g., a = 4, b = 3, c = 1. Then each bracket becomes 0, making the expression 0 immediately.



Why Other Options Are Wrong:
Any nonzero value would contradict the identity when p + q + r = 0.



Common Pitfalls:
Forgetting the shift and computing cubes of a, b, c directly; or using incorrect variations of the identity.



Final Answer:
0

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