Derivative of \( \displaystyle \frac{5 \ln{\left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)} \right)}}{3} \)
Problem 2.1233 · hard Video
Differentiate \( \displaystyle f(x) = \frac{5 \ln{\left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)} \right)}}{3} \).
- \[ \frac{d}{d x} \frac{5 \ln{\left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)} \right)}}{3} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{5 \frac{d}{d x} \ln{\left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)} \right)}}{3} \]constant-multiplePull out the constant factor.✓ Proved
- \[ = \frac{5 \frac{d}{d x} \left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}\right)}{3 \left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}\right)} \]logarithmicApply the chain rule for the natural logarithm.✓ Proved
- \[ = \frac{5 \left(\frac{d}{d x} \tan{\left(3 x + 1 \right)} + \frac{d}{d x} \sec{\left(3 x + 1 \right)}\right)}{3 \left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}\right)} \]sumApply the sum rule to the derivative.✓ Proved
- \[ = \frac{5 \left(3 \tan{\left(3 x + 1 \right)} \sec{\left(3 x + 1 \right)} + 3 \sec^{2}{\left(3 x + 1 \right)}\right)}{3 \left(\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}\right)} \]chainApply the chain rule to both tan and sec terms.≈ Checked numerically
- \[ = \frac{5 \left(\tan{\left(3 x + 1 \right)} \sec{\left(3 x + 1 \right)} + \sec^{2}{\left(3 x + 1 \right)}\right)}{\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}} \]constant-multipleFactor out the common constant 3.✓ Proved
- \[ = \frac{5 \tan{\left(3 x + 1 \right)} \sec{\left(3 x + 1 \right)} + 5 \sec^{2}{\left(3 x + 1 \right)}}{\tan{\left(3 x + 1 \right)} + \sec{\left(3 x + 1 \right)}} \]algebraSimplify the expression by multiplying the constants.✓ Proved
- \[ = 5 \sec{\left(3 x + 1 \right)} \]algebra simplifyFactor out sec(3*x + 1) from the numerator. Cancel the common term in the numerator and denominator.✓ Proved
Answer \( \frac{5}{\cos{\left(3 x + 1 \right)}} \)
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.
Lines: 9 proved, 1 checked numerically. 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 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 5 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left 5*(tan(3*x + 1)**2 - sec(3*x + 1)**2 + 1)/(tan(3*x + 1) + sec(3*x + 1)); numeric agreement only, at 24 of 24 sampled points tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 undefined where tan(3*x + 1) + sec(3*x + 1) = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 sec has poles at odd multiples of pi/2 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 undefined where cos(3*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: passqwen3.6:27b-mlx: pass — The solution correctly applies differentiation rules and algebraic simplifications in single-step increments. The labels accurately reflect the operations performed.
Every verdict on record (6)
qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies differentiation rules and algebraic simplifications in single-step increments. The labels accurately reflect the operations performed.gpt-oss:20b: pass 2026-10-03qwen3.6:27b-mlx: pass 2026-09-29 — The solution correctly applies differentiation rules and algebraic simplifications. Each step changes only one aspect of the expression, and the labels accurately reflect the operations performed.gpt-oss:20b: pass 2026-09-29qwen3.6:27b-mlx: pass 2026-09-29 — The solution correctly applies differentiation rules and algebraic simplifications in single-step increments. The labels accurately reflect the operations performed at each stage.gpt-oss:20b: fail (error) 2026-09-29 — Step 5 applies the chain rule to both the tan and sec terms in a single line, combining two separate rule applications into one step. This violates the rule that each step must change only one thing and apply only one named rule.
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.