∫Calc Practice

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

Problem 2.1206 · hard

Differentiate \( \displaystyle f(x) = - x \ln{\left(2 x + 1 \right)} + x - \frac{\ln{\left(2 x + 1 \right)}}{2} \).
  1. \[ \frac{d}{d x} \left(- x \ln{\left(2 x + 1 \right)} + x - \frac{\ln{\left(2 x + 1 \right)}}{2}\right) \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} x + \frac{d}{d x} \left(- x \ln{\left(2 x + 1 \right)}\right) - \frac{d}{d x} \frac{\ln{\left(2 x + 1 \right)}}{2} \]
    sumApply the sum rule.✓ Proved
  3. \[ = \frac{d}{d x} \left(- x \ln{\left(2 x + 1 \right)}\right) - \frac{d}{d x} \frac{\ln{\left(2 x + 1 \right)}}{2} + 1 \]
    derivativeDifferentiate the term x.✓ Proved
  4. \[ = \frac{d}{d x} \left(- x \ln{\left(2 x + 1 \right)}\right) - \frac{\frac{d}{d x} \ln{\left(2 x + 1 \right)}}{2} + 1 \]
    constant-multiplePull out the constant factor 1/2.✓ Proved
  5. \[ = - x \frac{d}{d x} \ln{\left(2 x + 1 \right)} + \ln{\left(2 x + 1 \right)} \frac{d}{d x} \left(- x\right) - \frac{\frac{d}{d x} \ln{\left(2 x + 1 \right)}}{2} + 1 \]
    productApply the product rule to the first term.✓ Proved
  6. \[ = - x \frac{d}{d x} \ln{\left(2 x + 1 \right)} - \ln{\left(2 x + 1 \right)} - \frac{\frac{d}{d x} \ln{\left(2 x + 1 \right)}}{2} + 1 \]
    derivative algebraDifferentiate -x. Simplify the coefficient.✓ Proved
  7. \[ = - \left(x + \frac{1}{2}\right) \frac{d}{d x} \ln{\left(2 x + 1 \right)} - \ln{\left(2 x + 1 \right)} + 1 \]
    algebraGroup the terms containing the derivative.✓ Proved
  8. \[ = - \frac{\left(x + \frac{1}{2}\right) \frac{d}{d x} \left(2 x + 1\right)}{2 x + 1} - \ln{\left(2 x + 1 \right)} + 1 \]
    chainApply the chain rule to the logarithm.✓ Proved
  9. \[ = - \frac{2 \left(x + \frac{1}{2}\right)}{2 x + 1} - \ln{\left(2 x + 1 \right)} + 1 \]
    derivativeDifferentiate the inner function 2*x + 1.✓ Proved
  10. \[ = - \ln{\left(2 x + 1 \right)} \]
    algebra algebra algebraSimplify the product (x + 1/2) * (2 / (2x + 1)). Simplify the fraction. Final simplification.✓ Proved
Answer \( - \ln{\left(2 x + 1 \right)} \)

✓ 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
log is undefined for non-positive arguments
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
13✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
log is undefined for non-positive arguments
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 differentiation rules one at a time with appropriate labels. The algebraic simplifications are sound and clearly explained.
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-09-29 — The solution correctly applies differentiation rules one at a time with appropriate labels. The algebraic simplifications are sound and clearly explained.
  • gpt-oss:20b: pass 2026-09-29
  • qwen3.6:27b-mlx: pass 2026-09-29
  • gpt-oss:20b: pass 2026-09-29

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 2026-09-29 with SymPy 1.14.0.