Difficulty: Medium
Correct Answer: 5
Explanation:
Introduction / Context:
The expression matches the well-known identity a^3 + b^3 + c^3 − 3abc = (a + b + c)(a^2 + b^2 + c^2 − ab − bc − ca). When the numerator and denominator are arranged in this exact pattern, the quotient simplifies dramatically to a + b + c, provided a + b + c ≠ 0.
Given Data / Assumptions:
Concept / Approach:
Recognize the factorization and cancel the common factor (a^2 + b^2 + c^2 − ab − bc − ca) from numerator and denominator, leaving just a + b + c.
Step-by-Step Solution:
Verification / Alternative check:
Expanding the right-hand side (a + b + c)(a^2 + b^2 + c^2 − ab − bc − ca) reproduces the numerator, confirming the identity holds regardless of decimal values.
Why Other Options Are Wrong:
1.730 and 5.247 are partial sums; 4 is a rounded guess; 3 ignores the identity. Only 5 equals a + b + c.
Common Pitfalls:
Not spotting the identity and attempting long decimal expansions or mishandling negative signs in the −ab − bc − ca terms.
Final Answer:
5
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