Algebraic identity under the condition a + b + c = 0 Evaluate the product: [(a + b)/c + (b + c)/a + (c + a)/b] × [a/(b + c) + b/(c + a) + c/(a + b)].

Difficulty: Medium

Correct Answer: 9

Explanation:


Introduction / Context:
This algebra question probes symmetry and substitution when a + b + c = 0. Recognizing how this constraint transforms compound fractions allows a short, elegant evaluation without heavy computation.



Given Data / Assumptions:

  • a + b + c = 0 (none of a, b, c, or their pairwise sums are zero in denominators unless expressly implied by the identity).
  • Target expression: S1 × S2 where S1 = (a + b)/c + (b + c)/a + (c + a)/b and S2 = a/(b + c) + b/(c + a) + c/(a + b).


Concept / Approach:
From a + b + c = 0, we have a + b = −c, b + c = −a, and c + a = −b. Substitute these into each fraction to simplify immediately.



Step-by-Step Solution:
S1 termwise: (a + b)/c = (−c)/c = −1; (b + c)/a = (−a)/a = −1; (c + a)/b = (−b)/b = −1.Hence S1 = (−1) + (−1) + (−1) = −3.S2 termwise: a/(b + c) = a/(−a) = −1; b/(c + a) = b/(−b) = −1; c/(a + b) = c/(−c) = −1.Hence S2 = (−1) + (−1) + (−1) = −3.Product: S1 × S2 = (−3) * (−3) = 9.



Verification / Alternative check:
Pick a simple triple satisfying a + b + c = 0, e.g., a = 1, b = 2, c = −3, and evaluate numerically to confirm S1 = S2 = −3.



Why Other Options Are Wrong:
0, 8, −3, and 3 ignore the paired substitutions that force each sum to −3; only the product 9 matches.



Common Pitfalls:
Forgetting that b + c = −a, etc.; attempting to find a common denominator instead of using the given linear constraint for direct simplification.



Final Answer:
9


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