Derivative of \( \displaystyle - \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \)
Problem 2.169 · medium
Differentiate \( \displaystyle f(x) = - \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \).
- \[ \frac{d}{d x} \left(- \frac{\sqrt{\left(2 x - 1\right)^{2} + 1}}{2}\right) \]Start with the derivative of the function.✓ Proved
- \[ = - \frac{\frac{d}{d x} \sqrt{\left(2 x - 1\right)^{2} + 1}}{2} \]constant rewritePull out the constant factor -1/2. Rewrite the square root as a fractional power.✓ Proved
- \[ = - \frac{\frac{d}{d x} \left(\left(2 x - 1\right)^{2} + 1\right)}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]chain algebraApply the chain rule. Multiply the constants.✓ Proved
- \[ = - \frac{\left(4 x - 2\right) \frac{d}{d x} \left(2 x - 1\right)}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]powerApply the power rule to the inner squared term.✓ Proved
- \[ = - \frac{8 x - 4}{4 \sqrt{\left(2 x - 1\right)^{2} + 1}} \]derivative algebraDifferentiate the innermost linear term. Simplify the product of constants.✓ Proved
- \[ = \frac{1 - 2 x}{\sqrt{\left(2 x - 1\right)^{2} + 1}} \]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
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 undefined where (2*x - 1)**2 + 1 = 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passdeepseek-r1:70b: passqwen3.6:27b-mlx: pass
Every verdict on record (15)
qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: pass 2026-09-20qwen3.6:27b-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 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-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 2026-09-19qwen3.6:27b-mlx: pass 2026-09-18deepseek-r1:70b: pass 2026-09-18gpt-oss:20b: pass 2026-09-18gpt-oss:20b: pass 2026-09-17deepseek-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.