∫Calc Practice
Home›Calculus 1›Chain rule›Problem 2.81

Derivative of \( \displaystyle x e^{2 x + 1} \)

Problem 2.81 · hard

Differentiate \( \displaystyle f(x) = x e^{2 x + 1} \).
  1. \[ \frac{d}{d x} x e^{2 x + 1} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = x \frac{d}{d x} e^{2 x + 1} + e^{2 x + 1} \frac{d}{d x} x \]
    productApply the product rule.✓ Proved
  3. \[ = x \frac{d}{d x} e^{2 x + 1} + e^{2 x + 1} \]
    derivative constantDifferentiate the first part of the product. The derivative of x is 1.✓ Proved
  4. \[ = x e^{2 x + 1} \frac{d}{d x} \left(2 x + 1\right) + e^{2 x + 1} \]
    chainApply the chain rule to the exponential term.✓ Proved
  5. \[ = 2 x e^{2 x + 1} + e^{2 x + 1} \]
    derivative algebraDifferentiate the inner function 2*x + 1. Rearrange the terms.✓ Proved
  6. \[ = \left(2 x + 1\right) e^{2 x + 1} \]
    simplifyFactor out the common exponential term.✓ Proved
Answer \( \left(2 x + 1\right) e^{2 x + 1} \)

✓ 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
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
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 (style) — Step 4 is labeled "constant" but it is a simplification (algebraic cancellation of 1*exp). The correct label should be "algebra" or "simplify".
  • deepseek-r1:70b: pass
  • qwen3.6:27b-mlx: pass
Every verdict on record (12)
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: fail (style) 2026-09-20 — Step 4 is labeled "constant" but it is a simplification (algebraic cancellation of 1*exp). The correct label should be "algebra" or "simplify".
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20 — Step 4 uses the label "constant" for a simplification of 1*exp(2*x+1); the correct label should be "algebra" or "simplify". All other steps are correct and properly labeled.
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: fail (style) 2026-09-19 — Step 4 incorrectly labels the differentiation of x as "constant"; it should be labeled "derivative". No other steps violate the contract.
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: fail (style) 2026-09-19 — Step 4 incorrectly labels the derivative of x as "constant"; the correct rule name is "derivative".
  • gpt-oss:20b: pass 2026-09-17
  • deepseek-r1:70b: pass 2026-09-17

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 2026-09-26 with SymPy 1.14.0.