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Derivative of \( \displaystyle \left(x + \frac{1}{5}\right) e^{5 x + 2} \)

Problem 2.1295 · medium

Differentiate \( \displaystyle f(x) = \left(x + \frac{1}{5}\right) e^{5 x + 2} \).
  1. \[ \frac{d}{d x} \left(x + \frac{1}{5}\right) e^{5 x + 2} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} x e^{5 x + 2} + \frac{d}{d x} \frac{e^{5 x + 2}}{5} \]
    sumApply the sum rule.✓ Proved
  3. \[ = \frac{d}{d x} x e^{5 x + 2} + \frac{\frac{d}{d x} e^{5 x + 2}}{5} \]
    constant-multipleApply the constant multiple rule to the second term.✓ Proved
  4. \[ = x \frac{d}{d x} e^{5 x + 2} + e^{5 x + 2} \frac{d}{d x} x + \frac{\frac{d}{d x} e^{5 x + 2}}{5} \]
    productApply the product rule to the first term.✓ Proved
  5. \[ = x \frac{d}{d x} e^{5 x + 2} + e^{5 x + 2} + \frac{\frac{d}{d x} e^{5 x + 2}}{5} \]
    derivativeDifferentiate the first part of the product rule.✓ Proved
  6. \[ = x e^{5 x + 2} \frac{d}{d x} \left(5 x + 2\right) + e^{5 x + 2} + \frac{\frac{d}{d x} e^{5 x + 2}}{5} \]
    productApply the product rule to the second term.✓ Proved
  7. \[ = 5 x e^{5 x + 2} + e^{5 x + 2} + \frac{\frac{d}{d x} e^{5 x + 2}}{5} \]
    derivativeDifferentiate the inner function 5*x + 2.✓ Proved
  8. \[ = 5 x e^{5 x + 2} + \frac{e^{5 x + 2} \frac{d}{d x} \left(5 x + 2\right)}{5} + e^{5 x + 2} \]
    algebraRearrange the terms.✓ Proved
  9. \[ = 5 x e^{5 x + 2} + 2 e^{5 x + 2} \]
    derivative algebra algebraDifferentiate the inner function again. Simplify the constant multiplication. Combine like terms.✓ Proved
  10. \[ = \left(5 x + 2\right) e^{5 x + 2} \]
    algebraFactor out the common exponential term.✓ Proved
Answer \( \left(5 x + 2\right) e^{5 x + 2} \)

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. A reviewer's objection to the explanation stands; see the receipt.

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
3✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
4✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: fail (error) — Step 9 incorrectly applies a derivative to the term (1/5)*exp(5*x+2)*Derivative(5*x+2,x). That term should have been simplified to (1/5)*exp(5*x+2)*5 in step 7, not differentiated again. This violates the rule that each step changes only one thing and mislabels the operation.
  • qwen3.6:27b-mlx: fail (error) — Step 6 is labeled 'product' but applies the chain rule to differentiate exp(5*x + 2). Step 8 is labeled 'algebra' but applies the chain rule to the third term. These steps mix rules or mislabel the chain rule application.
Every verdict on record (4)
  • qwen3.6:27b-mlx: fail (error) 2026-10-03 — Step 6 is labeled 'product' but applies the chain rule to differentiate exp(5*x + 2). Step 8 is labeled 'algebra' but applies the chain rule to the third term. These steps mix rules or mislabel the chain rule application.
  • gpt-oss:20b: fail (error) 2026-10-03 — Step 9 incorrectly applies a derivative to the term (1/5)*exp(5*x+2)*Derivative(5*x+2,x). That term should have been simplified to (1/5)*exp(5*x+2)*5 in step 7, not differentiated again. This violates the rule that each step changes only one thing and mislabels the operation.
  • qwen3.6:27b-mlx: fail (error) 2026-09-30 — Step 6 is labeled 'product' but applies the chain rule to differentiate the exponential function. Step 8 is labeled 'algebra' but performs differentiation (chain rule) on the third term, which is a mathematical error in labeling and logic.
  • gpt-oss:20b: fail (error) 2026-09-30 — Step 6 incorrectly applies the product rule to the derivative of exp(5*x+2); it should use the chain rule. Subsequent steps double‑count the derivative of the inner function, leading to an incorrect final expression.

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.