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Derivative of \( \displaystyle \frac{x}{x + 1} \)

Problem 2.12 · medium

Differentiate \( \displaystyle f(x) = \frac{x}{x + 1} \).
  1. \[ \frac{d}{d x} \frac{x}{x + 1} \]
    rewriteStart with the derivative of the function. Rewrite the fraction using a negative exponent.✓ Proved
  2. \[ = x \frac{d}{d x} \frac{1}{x + 1} + \frac{\frac{d}{d x} x}{x + 1} \]
    productApply the product rule.✓ Proved
  3. \[ = x \frac{d}{d x} \frac{1}{x + 1} + \frac{1}{x + 1} \]
    derivativeDifferentiate the first part of the product.✓ Proved
  4. \[ = - \frac{x \frac{d}{d x} \left(x + 1\right)}{\left(x + 1\right)^{2}} + \frac{1}{x + 1} \]
    chainApply the chain rule to the second part.✓ Proved
  5. \[ = - \frac{x}{\left(x + 1\right)^{2}} + \frac{1}{x + 1} \]
    derivative algebra rewrite algebraDifferentiate the inner function (x + 1). Simplify the expression. Rewrite the terms with positive exponents. Find a common denominator.✓ Proved
  6. \[ = \frac{1}{\left(x + 1\right)^{2}} \]
    algebra simplifyCombine the numerators. Simplify the final expression.✓ Proved
Answer \( \frac{1}{\left(x + 1\right)^{2}} \)

✓ Nihil obstat Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation.

The full receipt
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where x + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where x + 1 = 0
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • deepseek-r1:70b: fail (style) — Step 1 lacks a rule label, which is required by the contract.
  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass — The solution correctly applies the product and chain rules with appropriate labels. Each step changes only one aspect of the expression, adhering to the single-rule constraint.
Every verdict on record (14)
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product and chain rules with appropriate labels. Each step changes only one aspect of the expression, adhering to the single-rule constraint.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: fail (style) 2026-09-19 — Step 1 lacks a rule label, which is required by the contract.
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-18
  • deepseek-r1:70b: pass 2026-09-18
  • gpt-oss:20b: pass 2026-09-18
  • deepseek-r1:70b: pass 2026-09-16

Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence, not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by gemma4:26b, checked 2026-09-26 with SymPy 1.14.0.