Derivative of \( \displaystyle \left(2 x + 1\right)^{2 x} \)
Problem 2.366 · medium
Differentiate \( \displaystyle f(x) = \left(2 x + 1\right)^{2 x} \).
- \[ \frac{d}{d x} \left(2 x + 1\right)^{2 x} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} e^{2 x \ln{\left(2 x + 1 \right)}} \]rewriteRewrite the base and exponent using the exponential and logarithm.≈ Checked numerically
- \[ = e^{2 x \ln{\left(2 x + 1 \right)}} \frac{d}{d x} 2 x \ln{\left(2 x + 1 \right)} \]chainApply the chain rule for the exponential function.✓ Proved
- \[ = \left(2 x \frac{d}{d x} \ln{\left(2 x + 1 \right)} + \ln{\left(2 x + 1 \right)} \frac{d}{d x} 2 x\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]productApply the product rule to the inner expression.✓ Proved
- \[ = \left(2 x \frac{d}{d x} \ln{\left(2 x + 1 \right)} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]derivativeDifferentiate 2*x.✓ Proved
- \[ = \left(\frac{2 x \frac{d}{d x} \left(2 x + 1\right)}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]derivativeDifferentiate the logarithm using the chain rule.✓ Proved
- \[ = \left(\frac{4 x}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) e^{2 x \ln{\left(2 x + 1 \right)}} \]derivative algebraDifferentiate 2*x + 1. Simplify the expression inside the parentheses.✓ Proved
- \[ = \left(2 x + 1\right)^{2 x} \left(\frac{4 x}{2 x + 1} + 2 \ln{\left(2 x + 1 \right)}\right) \]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
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | ≈ Checked numerically | sympy 1.14.0 | sympy 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 | ✓ 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 undefined where 2*x + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 log is undefined for non-positive arguments undefined where 2*x + 1 = 0 |
| 9 | ≈ Checked numerically | sympy 1.14.0 | sympy 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 | ✓ Proved | sympy 1.14.0 | final 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 | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passdeepseek-r1:70b: passqwen3.6:27b-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 2026-09-20qwen3.6:27b-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 2026-09-20qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-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 2026-09-19gpt-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.