Recover and solve the intended equation (repair applied): Interpret the corrupted stem as ( (x + 4) / (x − 4) ) + ( (x − 4) / (x + 4) ) = 10 / 3. Find all real roots x.

Difficulty: Medium

Correct Answer: ± 8

Explanation:


Introduction / Context:
The original database text was garbled. Using the Recovery-First Policy, we interpret it as a classic rational-expression identity: (x + 4)/(x − 4) + (x − 4)/(x + 4) = 10/3. This kind of expression simplifies via a common denominator, producing an equation only in x^2. We then solve for x and check domain restrictions (x ≠ ±4).


Given Data / Assumptions:

  • (x + 4)/(x − 4) + (x − 4)/(x + 4) = 10/3.
  • Domain: x ≠ 4, x ≠ −4 (to avoid zero denominators).


Concept / Approach:
Use the identity (A/B) + (B/A) = (A^2 + B^2)/(AB). Here, A = x + 4 and B = x − 4. This yields a rational equation in x that simplifies to a quadratic in x^2. Solve and select the real roots allowed by the domain.


Step-by-Step Solution:

(x + 4)/(x − 4) + (x − 4)/(x + 4) = [(x + 4)^2 + (x − 4)^2]/(x^2 − 16) Numerator = (x^2 + 8x + 16) + (x^2 − 8x + 16) = 2x^2 + 32 So (2x^2 + 32)/(x^2 − 16) = 10/3 Cross-multiply: 3(2x^2 + 32) = 10(x^2 − 16) ⇒ 6x^2 + 96 = 10x^2 − 160 Rearrange: 4x^2 = 256 ⇒ x^2 = 64 ⇒ x = ±8


Verification / Alternative check:
Denominator check: x ≠ ±4, so ±8 are valid. Substitute x = 8 (or −8) to confirm the left-hand side equals 10/3 numerically.


Why Other Options Are Wrong:
±4 are excluded (division by zero). ±6 and 2 ± √3 do not satisfy the equation when substituted. “No real root” is false since ±8 work.


Common Pitfalls:
Dropping the domain restriction, or algebra errors when simplifying the rational sum can lead to spurious answers.


Final Answer:
± 8

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