If \frac{p+q}{q+r} = \frac{r+s}{s+p}; (q+r) \neq 0, (s+p) \neq 0, then which one of the following is correct?

  1. A. p + q + r + s = 0
  2. B. p = r
  3. C. Either p + q + r + s = 0 or p = r
  4. D. None of the above

Correct Answer: C. Either p + q + r + s = 0 or p = r

Explanation

Cross multiplying yields (p+q)(s+p) = (q+r)(r+s). Expanding gives ps + p^2 + qs + pq = qr + qs + r^2 + rs. Rearranging terms, p^2 - r^2 + ps + pq - qr - rs = 0, which factors into (p-r)(p+q+r+s) = 0. Hence, either p=r or p+q+r+s=0.

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