∫Calc Practice
Home›Calculus 1›Chain rule›Problem 2.1454

Derivative of \( \displaystyle \ln{\left(\frac{e^{3 x + 1}}{3 x + 1} \right)} \)

Problem 2.1454 · hard

Differentiate \( \displaystyle f(x) = \ln{\left(\frac{e^{3 x + 1}}{3 x + 1} \right)} \).
  1. \[ \frac{d}{d x} \ln{\left(\frac{e^{3 x + 1}}{3 x + 1} \right)} \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(3 x - \ln{\left(3 x + 1 \right)} + 1\right) \]
    logarithmic simplifyUse the property log(a/b) = log(a) - log(b). Simplify log(exp(3*x + 1)) to 3*x + 1.✓ Proved
  3. \[ = \frac{d}{d x} \left(3 x + 1\right) - \frac{d}{d x} \ln{\left(3 x + 1 \right)} \]
    sumSplit the derivative into two parts.✓ Proved
  4. \[ = 3 - \frac{d}{d x} \ln{\left(3 x + 1 \right)} \]
    constantThe derivative of 3*x + 1 is 3.✓ Proved
  5. \[ = 3 - \frac{\frac{d}{d x} \left(3 x + 1\right)}{3 x + 1} \]
    chainApply the chain rule to the logarithm.✓ Proved
  6. \[ = 3 - \frac{3}{3 x + 1} \]
    derivative algebraThe derivative of 3*x + 1 is 3. Simplify the expression.✓ Proved
  7. \[ = \frac{9 x}{3 x + 1} \]
    algebra algebra simplifyFind a common denominator. Distribute the 3. Simplify the numerator.✓ Proved
Answer \( \frac{9 x}{3 x + 1} \)
Mind the domain. The answer is also defined on (-oo, -1/3), where f(x) is not. Substituting there gives a number that is not a slope of f.

✓ 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 3*x + 1 = 0
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
undefined where 3*x + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x + 1 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x + 1 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x + 1 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where 3*x + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where 3*x + 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 logarithmic properties to simplify the function before differentiation, and each step adheres to the single-rule constraint with appropriate labels.
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies logarithmic properties to simplify the function before differentiation, and each step adheres to the single-rule constraint with appropriate labels.
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03

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 2026-10-03 with SymPy 1.14.0.