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Derivative of \( \displaystyle \frac{4 x^{2} - 1}{4 x^{2} + 1} \)

Problem 2.496 · hard

Differentiate \( \displaystyle f(x) = \frac{4 x^{2} - 1}{4 x^{2} + 1} \).
  1. \[ \frac{d}{d x} \frac{4 x^{2} - 1}{4 x^{2} + 1} \]
    rewriteStart with the derivative of the function. Rewrite the quotient as a product using a negative exponent.✓ Proved
  2. \[ = \left(4 x^{2} - 1\right) \frac{d}{d x} \frac{1}{4 x^{2} + 1} + \frac{\frac{d}{d x} \left(4 x^{2} - 1\right)}{4 x^{2} + 1} \]
    productApply the product rule.✓ Proved
  3. \[ = \frac{\left(1 - 4 x^{2}\right) \frac{d}{d x} \left(4 x^{2} + 1\right)}{\left(4 x^{2} + 1\right)^{2}} + \frac{\frac{d}{d x} \left(4 x^{2} - 1\right)}{4 x^{2} + 1} \]
    chainApply the chain rule to the second term.✓ Proved
  4. \[ = \frac{8 x \left(1 - 4 x^{2}\right)}{\left(4 x^{2} + 1\right)^{2}} + \frac{8 x}{4 x^{2} + 1} \]
    derivativeDifferentiate the polynomial terms.✓ Proved
  5. \[ = - \frac{8 x \left(4 x^{2} - 1\right)}{\left(4 x^{2} + 1\right)^{2}} + \frac{8 x}{4 x^{2} + 1} \]
    algebraSimplify the expression using negative exponents.✓ Proved
  6. \[ = \frac{- 8 x \left(4 x^{2} - 1\right) + 8 x \left(4 x^{2} + 1\right)}{\left(4 x^{2} + 1\right)^{2}} \]
    algebraCombine the terms over a common denominator.✓ Proved
  7. \[ = \frac{16 x}{\left(4 x^{2} + 1\right)^{2}} \]
    algebra simplifyDistribute the 8*x in the numerator. Simplify the numerator by combining like terms.✓ Proved
Answer \( \frac{16 x}{\left(4 x^{2} + 1\right)^{2}} \)

✓ 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 4*x**2 + 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where 4*x**2 + 1 = 0
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass — The solution correctly applies the product and chain rules, and the algebraic simplifications are sound. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
Every verdict on record (6)
  • qwen3.6:27b-mlx: pass 2026-09-21 — The solution correctly applies the product and chain rules, and the algebraic simplifications are sound. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-09-21
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule, chain rule, and algebraic simplifications. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product and chain rules, and the algebraic simplification steps are valid. Each step changes only one aspect of the expression and uses an appropriate label from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-09-20

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.