∫Calc Practice

Derivative of \( \displaystyle \ln{\left(e^{x + 1} + 1 \right)} \)

Problem 2.435 · hard

Differentiate \( \displaystyle f(x) = \ln{\left(e^{x + 1} + 1 \right)} \).
  1. \[ \frac{d}{d x} \ln{\left(e^{x + 1} + 1 \right)} \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{\frac{d}{d x} \left(e^{x + 1} + 1\right)}{e^{x + 1} + 1} \]
    chainApply the chain rule for the logarithm.✓ Proved
  3. \[ = \frac{\frac{d}{d x} 1 + \frac{d}{d x} e^{x + 1}}{e^{x + 1} + 1} \]
    sumApply the sum rule to the inner expression.✓ Proved
  4. \[ = \frac{\frac{d}{d x} e^{x + 1}}{e^{x + 1} + 1} \]
    constant algebraThe derivative of a constant is zero. Simplify the expression.✓ Proved
  5. \[ = \frac{e^{x + 1}}{e^{x + 1} + 1} \]
    exponential algebraDifferentiate the exponential function. Combine the terms into a single fraction.✓ Proved
Answer \( \frac{e^{x + 1}}{e^{x + 1} + 1} \)

✓ 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
log is undefined for non-positive arguments
undefined where exp(x + 1) + 1 = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where exp(x + 1) + 1 = 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where exp(x + 1) + 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where exp(x + 1) + 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where exp(x + 1) + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where exp(x + 1) + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where exp(x + 1) + 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
Every verdict on record (6)
  • qwen3.6:27b-mlx: pass 2026-09-21
  • gpt-oss:20b: pass 2026-09-21
  • 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

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.