Derivative of \( \displaystyle \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \)
Problem 2.1456 · hard
Differentiate \( \displaystyle f(x) = \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \).
- \[ \frac{d}{d x} \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- 2 x - \ln{\left(\cos{\left(2 x - 1 \right)} \right)} + 1\right) \]simplify simplifyUse logarithm properties to split the quotient. Simplify the log(exp(...)) term.✓ Proved
- \[ = \frac{d}{d x} \left(1 - 2 x\right) + \frac{d}{d x} \left(- \ln{\left(\cos{\left(2 x - 1 \right)} \right)}\right) \]sumApply the sum rule for differentiation.✓ Proved
- \[ = \frac{d}{d x} \left(1 - 2 x\right) - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]constantFactor out the negative sign.✓ Proved
- \[ = \frac{d}{d x} 1 - \frac{d}{d x} 2 x - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]sumSplit the first term into two parts.✓ Proved
- \[ = - \frac{d}{d x} 2 x - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]constant algebraDifferentiate the constant term. Simplify the expression.✓ Proved
- \[ = - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} - 2 \]derivativeDifferentiate the 2*x term.✓ Proved
- \[ = -2 - \frac{\frac{d}{d x} \cos{\left(2 x - 1 \right)}}{\cos{\left(2 x - 1 \right)}} \]chainApply the chain rule to the logarithm.✓ Proved
- \[ = \frac{\sin{\left(2 x - 1 \right)} \frac{d}{d x} \left(2 x - 1\right)}{\cos{\left(2 x - 1 \right)}} - 2 \]chainApply the chain rule to the cosine term.✓ Proved
- \[ = \frac{2 \sin{\left(2 x - 1 \right)}}{\cos{\left(2 x - 1 \right)}} - 2 \]derivative algebraDifferentiate the linear inner function. Simplify the signs and coefficients.✓ Proved
- \[ = 2 \tan{\left(2 x - 1 \right)} - 2 \]simplifyUse the identity tan(u) = sin(u)/cos(u).✓ Proved
Answer \( 2 \tan{\left(2 x - 1 \right)} - 2 \)
✓ 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 undefined where cos(2*x - 1) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where cos(2*x - 1) = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(2*x - 1) = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(2*x - 1) = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(2*x - 1) = 0 |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(2*x - 1) = 0 tan 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 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: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-03gpt-oss:20b: pass 2026-10-03qwen3.6:27b-mlx: pass 2026-10-03 — The solution correctly applies differentiation rules and algebraic simplifications. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-03
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.