Home›Calculus 1›Chain rule›Problem 2.301

Derivative of \( \displaystyle \ln{\left(\ln{\left(x - 3 \right)} \right)} \)

Problem 2.301 · medium

Differentiate \( \displaystyle f(x) = \ln{\left(\ln{\left(x - 3 \right)} \right)} \).

\[ \frac{d}{d x} \ln{\left(\ln{\left(x - 3 \right)} \right)} \]
derivativeStart with the derivative of the function.✓ Proved
\[ = \frac{\frac{d}{d x} \ln{\left(x - 3 \right)}}{\ln{\left(x - 3 \right)}} \]
chainApply the chain rule for the outer logarithm.✓ Proved
\[ = \frac{\frac{d}{d x} \left(x - 3\right)}{\left(x - 3\right) \ln{\left(x - 3 \right)}} \]
chainApply the chain rule for the inner logarithm.✓ Proved
\[ = \frac{1}{\left(x - 3\right) \ln{\left(x - 3 \right)}} \]
derivative algebraDifferentiate the innermost term. Multiply the terms together.✓ Proved

Answer \( \frac{1}{\left(x - 3\right) \log{\left(x - 3 \right)}} \)

Mind the domain. The answer is also defined on (3, 4), 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

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 log is undefined for non-positive arguments undefined where log(x - 3) = 0
3	✓ Proved	sympy 1.14.0	simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where log(x - 3) = 0 undefined where x - 3 = 0
4	✓ Proved	sympy 1.14.0	simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where log(x - 3) = 0 undefined where x - 3 = 0
5	✓ Proved	sympy 1.14.0	simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where log(x - 3) = 0 undefined where x - 3 = 0
answer	✓ Proved	sympy 1.14.0	final line against the stated answer: simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where log(x - 3) = 0 undefined where x - 3 = 0
answer, a second way	✓ Proved	sympy 1.14.0	SymPy differentiated f directly and got the stated answer

Reviewers

gpt-oss:20b: pass
deepseek-r1:70b: pass
qwen3.6:27b-mlx: pass — The solution correctly applies the chain rule in successive steps, differentiating one layer at a time, and uses valid labels from the fixed vocabulary.

Every verdict on record (12)

qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the chain rule in successive steps, differentiating one layer at a time, and uses valid labels from the fixed vocabulary.
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
deepseek-r1:70b: pass 2026-09-19
gpt-oss:20b: pass 2026-09-19
qwen3.6:27b-mlx: pass 2026-09-19
deepseek-r1:70b: pass 2026-09-19
gpt-oss:20b: pass 2026-09-19
gpt-oss:20b: fail 2026-09-17 — The solution omits the domain restriction x>4 (since log(log(x-3)) requires x-3>1). Ignoring this branch‑cut is a defect.
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.