Derivative of \( \displaystyle \frac{2 x}{2 x + 1} \)
Problem 2.314 · medium
Differentiate \( \displaystyle f(x) = \frac{2 x}{2 x + 1} \).
- \[ \frac{d}{d x} \frac{2 x}{2 x + 1} \]derivative rewriteStart with the derivative of the function. Rewrite the quotient as a product using a negative exponent.✓ Proved
- \[ = 2 \frac{d}{d x} \frac{x}{2 x + 1} \]constant-multipleFactor out the constant 2.✓ Proved
- \[ = 2 x \frac{d}{d x} \frac{1}{2 x + 1} + \frac{2 \frac{d}{d x} x}{2 x + 1} \]productApply the product rule.✓ Proved
- \[ = 2 x \frac{d}{d x} \frac{1}{2 x + 1} + \frac{2}{2 x + 1} \]derivativeDifferentiate x.✓ Proved
- \[ = - \frac{2 x \frac{d}{d x} \left(2 x + 1\right)}{\left(2 x + 1\right)^{2}} + \frac{2}{2 x + 1} \]chainApply the chain rule to the second term.✓ Proved
- \[ = - \frac{4 x}{\left(2 x + 1\right)^{2}} + \frac{2}{2 x + 1} \]derivative algebra algebraDifferentiate the inner function 2*x + 1. Simplify the exponents and coefficients. Find a common denominator.✓ Proved
- \[ = \frac{2}{\left(2 x + 1\right)^{2}} \]algebra simplify algebraCombine the fractions. Simplify the numerator. Final simplification.✓ Proved
Answer \( \frac{2}{\left(2 x + 1\right)^{2}} \)
✓ 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
| 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 undefined where 2*x + 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x + 1 = 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 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
Every verdict on record (12)
qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies differentiation rules in a step-by-step manner, adhering to the single-change constraint and using valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the quotient rule via rewrite and product/chain rules. Each step isolates a single operation, and the labels accurately reflect the rules applied.deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the quotient rule via rewrite and product rule, followed by chain rule and algebraic simplification. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19gpt-oss:20b: pass 2026-09-17deepseek-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.