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Derivative of \( \displaystyle - \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \)

Problem 2.169 · medium

Differentiate \( \displaystyle f(x) = - \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \).
  1. \[ \frac{d}{d x} \left(- \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2}\right) \]
    Start with the derivative of the function.✓ Proved
  2. \[ = - \frac{\frac{d}{d x} \sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \]
    constant rewritePull out the constant factor -1/2. Rewrite the square root as a fractional power.✓ Proved
  3. \[ = - \frac{\frac{d}{d x} \left(\left(2 x - 1\right)^{2} + 1\right)}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]
    chain algebraApply the chain rule. Multiply the constants.✓ Proved
  4. \[ = - \frac{\left(4 x - 2\right) \frac{d}{d x} \left(2 x - 1\right)}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]
    powerApply the power rule to the inner squared term.✓ Proved
  5. \[ = - \frac{8 x - 4}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]
    derivative algebraDifferentiate the innermost linear term. Simplify the product of constants.✓ Proved
  6. \[ = \frac{1 - 2 x}{\sqrt{\left(2 x - 1\right)^{2} + 1}} \]
    simplifySimplify the final expression by combining terms.✓ Proved
Answer \( \frac{1 - 2 x}{\sqrt{\left(2 x - 1\right)^{2} + 1}} \)

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

Reviewers

  • gpt-oss:20b: pass
  • deepseek-r1:70b: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (15)
  • qwen3.6:27b-mlx: pass 2026-09-20
  • 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 — The solution correctly applies the chain rule, power rule, and constant multiple rule in a step-by-step manner. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the constant multiple, chain, and power rules in a logical sequence. Each step isolates a single transformation, and the labels accurately reflect the operations performed.
  • deepseek-r1:70b: fail (error) 2026-09-19 — Step 1 lacks a rule label, violating the contract.
  • 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
  • gpt-oss:20b: pass 2026-09-17
  • deepseek-r1:70b: pass 2026-09-17

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.