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Derivative of \( \displaystyle \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \)

Problem 2.1456 · hard

Differentiate \( \displaystyle f(x) = \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \).
  1. \[ \frac{d}{d x} \ln{\left(\frac{e^{1 - 2 x}}{\cos{\left(2 x - 1 \right)}} \right)} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} \left(- 2 x - \ln{\left(\cos{\left(2 x - 1 \right)} \right)} + 1\right) \]
    simplify simplifyUse logarithm properties to split the quotient. Simplify the log(exp(...)) term.✓ Proved
  3. \[ = \frac{d}{d x} \left(1 - 2 x\right) + \frac{d}{d x} \left(- \ln{\left(\cos{\left(2 x - 1 \right)} \right)}\right) \]
    sumApply the sum rule for differentiation.✓ Proved
  4. \[ = \frac{d}{d x} \left(1 - 2 x\right) - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]
    constantFactor out the negative sign.✓ Proved
  5. \[ = \frac{d}{d x} 1 - \frac{d}{d x} 2 x - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]
    sumSplit the first term into two parts.✓ Proved
  6. \[ = - \frac{d}{d x} 2 x - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} \]
    constant algebraDifferentiate the constant term. Simplify the expression.✓ Proved
  7. \[ = - \frac{d}{d x} \ln{\left(\cos{\left(2 x - 1 \right)} \right)} - 2 \]
    derivativeDifferentiate the 2*x term.✓ Proved
  8. \[ = -2 - \frac{\frac{d}{d x} \cos{\left(2 x - 1 \right)}}{\cos{\left(2 x - 1 \right)}} \]
    chainApply the chain rule to the logarithm.✓ Proved
  9. \[ = \frac{\sin{\left(2 x - 1 \right)} \frac{d}{d x} \left(2 x - 1\right)}{\cos{\left(2 x - 1 \right)}} - 2 \]
    chainApply the chain rule to the cosine term.✓ Proved
  10. \[ = \frac{2 \sin{\left(2 x - 1 \right)}}{\cos{\left(2 x - 1 \right)}} - 2 \]
    derivative algebraDifferentiate the linear inner function. Simplify the signs and coefficients.✓ Proved
  11. \[ = 2 \tan{\left(2 x - 1 \right)} - 2 \]
    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
LineStatusChecked byDetail
1✓ Provedsympy 1.14.0line 1 is the problem as stated
2✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where cos(2*x - 1) = 0
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where cos(2*x - 1) = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(2*x - 1) = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(2*x - 1) = 0
13✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(2*x - 1) = 0
14✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where cos(2*x - 1) = 0
tan has poles at odd multiples of pi/2
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
tan has poles at odd multiples of pi/2
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (4)
  • qwen3.6:27b-mlx: pass 2026-10-03
  • gpt-oss:20b: pass 2026-10-03
  • qwen3.6:27b-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.