∫Calc Practice

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

Problem 2.366 · medium

Differentiate \( \displaystyle f(x) = \left(2 x + 1\right)^{2 x} \).
  1. \[ \frac{d}{d x} \left(2 x + 1\right)^{2 x} \]
    derivativeStart with the derivative of the function.✓ Proved
  2. \[ = \frac{d}{d x} e^{2 x \ln{\left(2 x + 1 \right)}} \]
    rewriteRewrite the base and exponent using the exponential and logarithm.≈ Checked numerically
  3. \[ = e^{2 x \ln{\left(2 x + 1 \right)}} \frac{d}{d x} 2 x \ln{\left(2 x + 1 \right)} \]
    chainApply the chain rule for the exponential function.✓ Proved
  4. \[ = \left(2 x \frac{d}{d x} \ln{\left(2 x + 1 \right)} + \ln{\left(2 x + 1 \right)} \frac{d}{d x} 2 x\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]
    productApply the product rule to the inner expression.✓ Proved
  5. \[ = \left(2 x \frac{d}{d x} \ln{\left(2 x + 1 \right)} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]
    derivativeDifferentiate 2*x.✓ Proved
  6. \[ = \left(\frac{2 x \frac{d}{d x} \left(2 x + 1\right)}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]
    derivativeDifferentiate the logarithm using the chain rule.✓ Proved
  7. \[ = \left(\frac{4 x}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]
    derivative algebraDifferentiate 2*x + 1. Simplify the expression inside the parentheses.✓ Proved
  8. \[ = \left(2 x + 1\right)^{2 x} \left(\frac{4 x}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) \]
    simplifyConvert the exponential form back to the original power form.≈ Checked numerically
Answer \( \left(2 x + 1\right)^{2 x} \left(\frac{4 x}{2 x + 1} + 2 \log{\left(2 x + 1 \right)}\right) \)

✓ Nihil obstat Lines: 8 proved, 2 checked numerically. 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≈ Checked numericallysympy 1.14.0sympy 1.14.0: simplify left 2*(2*x + (2*x + 1)*log(2*x + 1))*((2*x + 1)**(2*x) - exp(2*x*log(2*x + 1)))/(2*x + 1); numeric agreement only, at 24 of 24 sampled points
log is undefined for non-positive arguments
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
undefined where 2*x + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
9≈ Checked numericallysympy 1.14.0sympy 1.14.0: simplify left 2*(2*x + (2*x + 1)*log(2*x + 1))*(-(2*x + 1)**(2*x) + exp(2*x*log(2*x + 1)))/(2*x + 1); numeric agreement only, at 24 of 24 sampled points
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
log is undefined for non-positive arguments
undefined where 2*x + 1 = 0
answer, a second way✓ Provedsympy 1.14.0SymPy differentiated f directly and got the stated answer

Reviewers

  • gpt-oss:20b: pass
  • deepseek-r1:70b: pass
  • qwen3.6:27b-mlx: pass — The solution correctly applies the chain rule, product rule, and standard derivatives in a logical sequence. Each step changes only one aspect of the expression and uses valid labels from the provided vocabulary.
Every verdict on record (10)
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the chain rule, product rule, and standard derivatives in a logical sequence. Each step changes only one aspect of the expression and uses valid labels from the provided vocabulary.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies logarithmic differentiation by rewriting the function, applying the chain rule, product rule, and standard derivatives in a step-by-step manner. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-19
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies logarithmic differentiation, adhering to the one-rule-per-step constraint and using valid labels from the fixed vocabulary.
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19

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.