Derivative of \( \displaystyle \frac{3 \ln{\left(\tan^{2}{\left(2 x - 3 \right)} + 1 \right)}}{4} \)
Problem 2.665 · hard
Differentiate \( \displaystyle f(x) = \frac{3 \ln{\left(\tan^{2}{\left(2 x - 3 \right)} + 1 \right)}}{4} \).
- \[ \frac{d}{d x} \frac{3 \ln{\left(\tan^{2}{\left(2 x - 3 \right)} + 1 \right)}}{4} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{3 \frac{d}{d x} \ln{\left(\tan^{2}{\left(2 x - 3 \right)} + 1 \right)}}{4} \]constant-multiplePull out the constant factor.✓ Proved
- \[ = \frac{3 \frac{d}{d x} \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)}{4 \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)} \]logarithmicApply the derivative rule for the natural logarithm.✓ Proved
- \[ = \frac{3 \left(\frac{d}{d x} 1 + \frac{d}{d x} \tan^{2}{\left(2 x - 3 \right)}\right)}{4 \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)} \]chainApply the chain rule to the inner function.✓ Proved
- \[ = \frac{3 \frac{d}{d x} \tan^{2}{\left(2 x - 3 \right)}}{4 \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)} \]constant algebraThe derivative of the constant 1 is 0. Simplify the expression by removing the zero term.✓ Proved
- \[ = \frac{3 \tan{\left(2 x - 3 \right)} \frac{d}{d x} \tan{\left(2 x - 3 \right)}}{2 \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)} \]powerApply the power rule to the squared tangent term.✓ Proved
- \[ = \frac{3 \tan{\left(2 x - 3 \right)} \sec^{2}{\left(2 x - 3 \right)} \frac{d}{d x} \left(2 x - 3\right)}{2 \left(\tan^{2}{\left(2 x - 3 \right)} + 1\right)} \]trigThe derivative of tan(u) is sec(u)^2 * du/dx.≈ Checked numerically
- \[ = \frac{3 \tan{\left(2 x - 3 \right)} \sec^{2}{\left(2 x - 3 \right)}}{\tan^{2}{\left(2 x - 3 \right)} + 1} \]chain algebra algebraDifferentiate the innermost linear function 2*x - 3. Multiply the constants together. Combine the terms into a single fraction.✓ Proved
- \[ = 3 \tan{\left(2 x - 3 \right)} \]simplifyUse the identity 1 + tan(u)^2 = sec(u)^2 to simplify the fraction.≈ Checked numerically
Answer \( 3 \tan{\left(2 x - 3 \right)} \)
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: 11 proved, 2 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 |
| 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 undefined where tan(2*x - 3)**2 + 1 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where tan(2*x - 3)**2 + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where tan(2*x - 3)**2 + 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where tan(2*x - 3)**2 + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 undefined where tan(2*x - 3)**2 + 1 = 0 |
| 8 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left 3*(tan(2*x - 3)**2 - sec(2*x - 3)**2 + 1)*tan(2*x - 3)/(tan(2*x - 3)**2 + 1); numeric agreement only, at 24 of 24 sampled points tan has poles at odd multiples of pi/2 undefined where tan(2*x - 3)**2 + 1 = 0 sec has poles at odd multiples of pi/2 |
| 9 | ✓ 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(2*x - 3)**2 + 1 = 0 |
| 10 | ✓ 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(2*x - 3)**2 + 1 = 0 |
| 11 | ✓ 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(2*x - 3)**2 + 1 = 0 |
| 12 | ≈ Checked numerically | sympy 1.14.0 | sympy 1.14.0: simplify left 3*(-tan(2*x - 3)**2 + sec(2*x - 3)**2 - 1)*tan(2*x - 3)/(tan(2*x - 3)**2 + 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(2*x - 3)**2 + 1 = 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 |
| 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 4 applies the sum rule but is labeled "chain"; the correct label should be "sum". No other mathematical errors are present.qwen3.6:27b-mlx: fail (style) — Step 4 is labeled 'chain' but applies the sum rule to split the derivative of a sum; it should be labeled 'sum'. Step 9 is labeled 'chain' but applies the power/linear rule to differentiate 2x-3; it should be labeled 'derivative' or 'algebra'.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (style) 2026-09-21 — Step 4 is labeled 'chain' but applies the sum rule to split the derivative of a sum; it should be labeled 'sum'. Step 9 is labeled 'chain' but applies the power/linear rule to differentiate 2x-3; it should be labeled 'derivative' or 'algebra'.gpt-oss:20b: fail (style) 2026-09-21 — Step 4 applies the sum rule but is labeled "chain"; the correct label should be "sum". No other mathematical errors are present.qwen3.6:27b-mlx: fail (style) 2026-09-21 — Step 4 is labeled 'chain' but applies the sum rule to split the derivative of a sum; it should be labeled 'sum'. Step 9 is labeled 'chain' but applies the derivative of a linear function; it should be labeled 'derivative'.gpt-oss:20b: fail (style) 2026-09-21 — Step 4 incorrectly labels the application of the sum rule as "chain". The derivative of tan(2*x-3)**2 + 1 should be split into the sum of derivatives, which is a "sum" step, not a "chain" step.
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.