Derivative of \( \displaystyle - \ln{\left(\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)} \right)} \)
Problem 2.1123 · hard Video
Differentiate \( \displaystyle f(x) = - \ln{\left(\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)} \right)} \).
- \[ \frac{d}{d x} \left(- \ln{\left(\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)} \right)}\right) \]Start with the derivative of the function.✓ Proved
- \[ = - \frac{d}{d x} \ln{\left(\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)} \right)} \]constantPull out the constant factor -1.✓ Proved
- \[ = - \frac{\frac{d}{d x} \left(\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)}\right)}{\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)}} \]chainApply the chain rule for the logarithm.✓ Proved
- \[ = - \frac{\frac{d}{d x} \cot{\left(5 x + 1 \right)} + \frac{d}{d x} \csc{\left(5 x + 1 \right)}}{\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)}} \]sumApply the sum rule to the inner expression.✓ Proved
- \[ = - \frac{- 5 \cot{\left(5 x + 1 \right)} \csc{\left(5 x + 1 \right)} - 5 \csc^{2}{\left(5 x + 1 \right)}}{\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)}} \]trig algebraDifferentiate the cotangent and cosecant terms using the chain rule. Factor out -5 from the derivative terms.✓ Proved
- \[ = \frac{5 \cot{\left(5 x + 1 \right)} \csc{\left(5 x + 1 \right)} + 5 \csc^{2}{\left(5 x + 1 \right)}}{\cot{\left(5 x + 1 \right)} + \csc{\left(5 x + 1 \right)}} \]algebraSimplify the expression by distributing the negative sign.✓ Proved
- \[ = 5 \csc{\left(5 x + 1 \right)} \]algebra simplifyFactor out csc(5*x + 1) in the numerator. Cancel the common term in the numerator and denominator.✓ Proved
Answer \( \frac{5}{\sin{\left(5 x + 1 \right)}} \)
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.
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. The reviewers disagree about how one step is explained; every verdict is in the receipt. How we verify
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 |
| 3 | ✓ 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(5*x + 1) + csc(5*x + 1) = 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(5*x + 1) + csc(5*x + 1) = 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(5*x + 1) + csc(5*x + 1) = 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(5*x + 1) + csc(5*x + 1) = 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(5*x + 1) + csc(5*x + 1) = 0 |
| 8 | ✓ 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(5*x + 1) + csc(5*x + 1) = 0 |
| 9 | ✓ 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(5*x + 1) = 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: fail (error) — Step 5 applies two differentiation rules at once (derivative of cot and derivative of csc, each involving a chain rule). The step should be split into two separate applications, each labeled appropriately.qwen3.6:27b-mlx: pass
Every verdict on record (6)
qwen3.6:27b-mlx: pass 2026-10-03gpt-oss:20b: fail (error) 2026-10-03 — Step 5 applies two differentiation rules at once (derivative of cot and derivative of csc, each involving a chain rule). The step should be split into two separate applications, each labeled appropriately.qwen3.6:27b-mlx: pass 2026-09-28gpt-oss:20b: pass 2026-09-28qwen3.6:27b-mlx: pass 2026-09-28gpt-oss:20b: fail (style) 2026-09-28 — Step 5 applies both the chain rule and the trig derivative rule in a single step, violating the rule that each step must change only one thing.
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.