Derivative of \( \displaystyle \frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \)
Problem 2.2127 · hard
Differentiate \( \displaystyle f(x) = \frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \).
- \[ \frac{d}{d x} \left(\frac{5 x^{2}}{4} + x - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)}\right) \]Start with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} - \frac{d}{d x} \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \ln{\left(5 x + 2 \right)} \]sumApply the sum rule.✓ Proved
- \[ = - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} - \ln{\left(5 x + 2 \right)} \frac{d}{d x} \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]productApply the product rule to the third term.✓ Proved
- \[ = - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} - \left(\frac{d}{d x} \frac{2}{5} + \frac{d}{d x} 2 x + \frac{d}{d x} \frac{5 x^{2}}{2}\right) \ln{\left(5 x + 2 \right)} + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]sumApply the sum rule to the first part of the product rule.✓ Proved
- \[ = - \left(\frac{d}{d x} 2 x + \frac{d}{d x} \frac{5 x^{2}}{2}\right) \ln{\left(5 x + 2 \right)} - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} + \frac{d}{d x} x + \frac{d}{d x} \frac{5 x^{2}}{4} \]constant sumThe derivative of the constant 2/5 is 0. Apply the sum rule to the inner terms.✓ Proved
- \[ = - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} - \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right) \frac{d}{d x} \ln{\left(5 x + 2 \right)} + \frac{d}{d x} \frac{5 x^{2}}{4} + 1 \]derivativeDifferentiate the simple terms.✓ Proved
- \[ = - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + \frac{d}{d x} \frac{5 x^{2}}{4} + 1 - \frac{5 \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right)}{5 x + 2} \]chain algebraApply the chain rule to the log term. Simplify the derivative of the log term.✓ Proved
- \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{5 \left(\frac{5 x^{2}}{2} + 2 x + \frac{2}{5}\right)}{5 x + 2} \]derivativeDifferentiate the first term.✓ Proved
- \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{\frac{25 x^{2}}{2} + 10 x + 2}{5 x + 2} \]algebraDistribute the 5 in the last term.✓ Proved
- \[ = \frac{5 x}{2} - \left(5 x + 2\right) \ln{\left(5 x + 2 \right)} + 1 - \frac{25 x^{2} + 20 x + 4}{10 x + 4} \]algebra algebra simplifySimplify the fraction. Expand the denominator. Final simplification of the expression.✓ Proved
Answer \( \left(- 5 x - 2\right) \ln{\left(5 x + 2 \right)} \)
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 undefined where 5*x + 2 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 5*x + 2 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 5*x + 2 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 5*x + 2 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 5*x + 2 = 0 undefined where 10*x + 4 = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 10*x + 4 = 0 |
| 14 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 10*x + 4 = 0 |
| 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: pass
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-12qwen3.6:27b-mlx: pass 2026-10-12gpt-oss:20b: fail (error) 2026-10-12 — Step 7 incorrectly replaces the derivative of 2*x with 1, changing two terms in one step and producing an incorrect result.qwen3.6:27b-mlx: fail (error) 2026-10-12 — The final answer provided in the task description is (-5*x - 2)*log(5*x + 2), but the solution steps derive 5*x/2 + 1 - (5*x + 2)*log(5*x + 2). The solution fails to simplify the rational term (25*x**2 + 20*x + 4)/(2*(5*x + 2)) to (5*x + 2)/2, which would cancel with the 5*x/2 + 1 terms to yield the stated answer. Thus, the steps do not lead to the stated answer.
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 2026-10-12 with SymPy 1.14.0.