Derivative of \( \displaystyle \ln{\left(- \cot{\left(3 x \right)} + \csc{\left(3 x \right)} \right)} \)
Problem 2.1828 · hard Beautiful
Differentiate \( \displaystyle f(x) = \ln{\left(- \cot{\left(3 x \right)} + \csc{\left(3 x \right)} \right)} \).
- \[ \frac{d}{d x} \ln{\left(- \cot{\left(3 x \right)} + \csc{\left(3 x \right)} \right)} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{\frac{d}{d x} \left(- \cot{\left(3 x \right)} + \csc{\left(3 x \right)}\right)}{- \cot{\left(3 x \right)} + \csc{\left(3 x \right)}} \]chainApply the chain rule for the natural logarithm.✓ Proved
- \[ = \frac{\frac{d}{d x} \left(- \cot{\left(3 x \right)}\right) + \frac{d}{d x} \csc{\left(3 x \right)}}{- \cot{\left(3 x \right)} + \csc{\left(3 x \right)}} \]sumApply the sum rule to the derivative of the inner expression.✓ Proved
- \[ = \frac{- \frac{d}{d x} \cot{\left(3 x \right)} + \frac{d}{d x} \csc{\left(3 x \right)}}{- \cot{\left(3 x \right)} + \csc{\left(3 x \right)}} \]constantFactor out the negative sign from the first term.✓ Proved
- \[ = \frac{- 3 \cot{\left(3 x \right)} \csc{\left(3 x \right)} + 3 \csc^{2}{\left(3 x \right)}}{- \cot{\left(3 x \right)} + \csc{\left(3 x \right)}} \]trig algebraDifferentiate the trigonometric functions using the chain rule. Simplify the expression by distributing the negative signs.✓ Proved
- \[ = 3 \csc{\left(3 x \right)} \]algebra simplifyFactor out the common term 3*csc(3*x) from the numerator. Cancel the common factor in the numerator and denominator.✓ Proved
Answer \( \frac{3}{\sin{\left(3 x \right)}} \)
Mind the domain. The answer is also defined at points 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 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi cot has poles at multiples of pi undefined where -cot(3*x) + csc(3*x) = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 csc has poles at multiples of pi |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 undefined where sin(3*x) = 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-08gpt-oss:20b: pass 2026-10-08gpt-oss:20b: pass 2026-10-08qwen3.6:27b-mlx: pass 2026-10-08
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 2026-10-08 with SymPy 1.14.0.