Derivative of \( \displaystyle \frac{5 \ln{\left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)} \right)}}{4} \)
Problem 2.950 · hard
Differentiate \( \displaystyle f(x) = \frac{5 \ln{\left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)} \right)}}{4} \).
- \[ \frac{d}{d x} \frac{5 \ln{\left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)} \right)}}{4} \]constant-multipleStart with the derivative of the function.✓ Proved
- \[ = \frac{5 \frac{d}{d x} \ln{\left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)} \right)}}{4} \]chainApply the chain rule to the logarithm.✓ Proved
- \[ = \frac{5 \frac{d}{d x} \left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}\right)}{4 \left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}\right)} \]sumDifferentiate the sum inside the parentheses.✓ Proved
- \[ = \frac{5 \left(\frac{d}{d x} \tan{\left(4 x - 3 \right)} + \frac{d}{d x} \sec{\left(4 x - 3 \right)}\right)}{4 \left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}\right)} \]chainApply the chain rule to each trigonometric term.✓ Proved
- \[ = \frac{5 \left(4 \tan{\left(4 x - 3 \right)} \sec{\left(4 x - 3 \right)} + 4 \sec^{2}{\left(4 x - 3 \right)}\right)}{4 \left(\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}\right)} \]constant-multipleDifferentiate the tangent and secant terms.≈ Checked numerically
- \[ = \frac{5 \left(\tan{\left(4 x - 3 \right)} \sec{\left(4 x - 3 \right)} + \sec^{2}{\left(4 x - 3 \right)}\right)}{\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}} \]algebraFactor out the constant 4.✓ Proved
- \[ = \frac{5 \tan{\left(4 x - 3 \right)} \sec{\left(4 x - 3 \right)} + 5 \sec^{2}{\left(4 x - 3 \right)}}{\tan{\left(4 x - 3 \right)} + \sec{\left(4 x - 3 \right)}} \]algebraSimplify the constant coefficients.✓ Proved
- \[ = 5 \sec{\left(4 x - 3 \right)} \]algebra simplifyFactor out sec(4*x - 3) from the numerator. Cancel the common factor in the numerator and denominator.✓ Proved
Answer \( \frac{5}{\cos{\left(4 x - 3 \right)}} \)
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 Lines: 9 proved, 1 checked numerically. 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 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(4*x - 3) + sec(4*x - 3) = 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(4*x - 3) + sec(4*x - 3) = 0 |
| 5 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left 5*(tan(4*x - 3)**2 - sec(4*x - 3)**2 + 1)/(tan(4*x - 3) + sec(4*x - 3)); 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(4*x - 3) + sec(4*x - 3) = 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(4*x - 3) + sec(4*x - 3) = 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(4*x - 3) + sec(4*x - 3) = 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(4*x - 3) + sec(4*x - 3) = 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(4*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: fail (style) — Step 5 labels the application of the chain rule as "constant-multiple". The derivative of tan(4*x-3) and sec(4*x-3) requires the chain rule, not a constant‑multiple rule. This mislabeling could mislead a student about which rule to apply.qwen3.6:27b-mlx: fail (style) — Step 3 is labeled 'sum' but performs the differentiation of the logarithm (chain rule/logarithmic rule), not just the sum rule. Step 5 is labeled 'constant-multiple' but performs the actual differentiation of tan and sec (derivative/chain rule), which is a mismatch between label and operation.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (style) 2026-09-27 — Step 3 is labeled 'sum' but performs the differentiation of the logarithm (chain rule/logarithmic rule), not just the sum rule. Step 5 is labeled 'constant-multiple' but performs the actual differentiation of tan and sec (derivative/chain rule), which is a mismatch between label and operation.gpt-oss:20b: fail (style) 2026-09-27 — Step 5 labels the application of the chain rule as "constant-multiple". The derivative of tan(4*x-3) and sec(4*x-3) requires the chain rule, not a constant‑multiple rule. This mislabeling could mislead a student about which rule to apply.qwen3.6:27b-mlx: fail (style) 2026-09-27 — Step 3 is labeled 'sum' but actually applies the chain rule to the logarithm (derivative of log(u) is u'/u). Step 5 is labeled 'constant-multiple' but actually computes the derivatives of tan and sec using the chain rule and standard derivative formulas.gpt-oss:20b: pass 2026-09-27
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 2026-09-27 with SymPy 1.14.0.