Derivative of \( \displaystyle - x + \ln{\left(\left(2 x\right)^{x} \right)} \)
Problem 2.1598 · hard
Differentiate \( \displaystyle f(x) = - x + \ln{\left(\left(2 x\right)^{x} \right)} \).
- \[ \frac{d}{d x} \left(- x + \ln{\left(\left(2 x\right)^{x} \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \ln{\left(\left(2 x\right)^{x} \right)} \]sumApply the sum rule.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \ln{\left(e^{x \ln{\left(2 x \right)}} \right)} \]rewriteRewrite the power using the exponential and logarithm identity.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} x \ln{\left(2 x \right)} \]simplifySimplify the log of the exponential.✓ Proved
- \[ = x \frac{d}{d x} \ln{\left(2 x \right)} + \ln{\left(2 x \right)} \frac{d}{d x} x + \frac{d}{d x} \left(- x\right) \]productApply the product rule to the term inside the derivative.✓ Proved
- \[ = x \frac{d}{d x} \ln{\left(2 x \right)} + \ln{\left(2 x \right)} + \frac{d}{d x} \left(- x\right) \]derivativeDifferentiate x.✓ Proved
- \[ = \ln{\left(2 x \right)} + \frac{d}{d x} \left(- x\right) + \frac{\frac{d}{d x} 2 x}{2} \]chainApply the chain rule to log(2*x).✓ Proved
- \[ = \ln{\left(2 x \right)} + \frac{d}{d x} \left(- x\right) + 1 \]derivative constant-multiple algebraDifferentiate 2*x. Simplify the constant multiplier. Simplify the expression inside the parentheses.✓ Proved
- \[ = \ln{\left(2 x \right)} \]derivative algebraDifferentiate -x and simplify. Combine the constant terms.✓ Proved
Answer \( \ln{\left(2 x \right)} \)
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. The reviewers disagree about how one step is explained; every verdict is in the receipt.
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 |
| 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 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| 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: fail (error) — Step 11 applies two rules at once: it differentiates -x (derivative rule) and simplifies the expression (algebra/simplify rule) in a single step, violating the one-rule-per-step constraint.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (error) 2026-10-05 — Step 11 applies two rules at once: it differentiates -x (derivative rule) and simplifies the expression (algebra/simplify rule) in a single step, violating the one-rule-per-step constraint.gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: fail (style) 2026-10-05 — Step 11 applies two rules at once: it differentiates -x (derivative rule) and simplifies the constant term 1+(-1) (algebra/simplify rule), violating the one-change-per-step constraint.gpt-oss:20b: pass 2026-10-05
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 2026-10-05 with SymPy 1.14.0.