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

Problem 2.102 · medium

Differentiate \( \displaystyle f(x) = \frac{\sqrt{\left(5 x + 1\right)^{2} + 1}}{5} \).
  1. \[ \frac{d}{d x} \frac{\sqrt{\left(5 x + 1\right)^{2} + 1}}{5} \]
    Start with the derivative of the function.✓ Proved
  2. \[ = \frac{\frac{d}{d x} \sqrt{\left(5 x + 1\right)^{2} + 1}}{5} \]
    constant rewritePull out the constant factor 1/5. Rewrite the square root as a power.✓ Proved
  3. \[ = \frac{\frac{d}{d x} \left(\left(5 x + 1\right)^{2} + 1\right)}{10 \sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    chain algebraApply the chain rule. Multiply the constants.✓ Proved
  4. \[ = \frac{\frac{d}{d x} 1 + \frac{d}{d x} \left(5 x + 1\right)^{2}}{10 \sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    sumDifferentiate the sum inside the parenthesis.✓ Proved
  5. \[ = \frac{\frac{d}{d x} \left(5 x + 1\right)^{2}}{10 \sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    constantThe derivative of the constant 1 is 0.✓ Proved
  6. \[ = \frac{\left(10 x + 2\right) \frac{d}{d x} \left(5 x + 1\right)}{10 \sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    chainApply the chain rule to the power term.✓ Proved
  7. \[ = \frac{50 x + 10}{10 \sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    derivative algebra algebraDifferentiate the inner linear term. Multiply the constants inside the parenthesis. Combine the terms into a single fraction.✓ Proved
  8. \[ = \frac{5 x + 1}{\sqrt{\left(5 x + 1\right)^{2} + 1}} \]
    simplifySimplify the fraction by canceling the 10.✓ Proved
Answer \( \frac{5 x + 1}{\sqrt{\left(5 x + 1\right)^{2} + 1}} \)

✓ 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
undefined where (5*x + 1)**2 + 1 = 0
5✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
6✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
7✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
8✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
9✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
10✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
11✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
12✓ Provedsympy 1.14.0simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 1 = 0
answer✓ Provedsympy 1.14.0final line against the stated answer: simplify(a - b) reduced to 0
undefined where (5*x + 1)**2 + 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
Every verdict on record (15)
  • qwen3.6:27b-mlx: pass 2026-09-20
  • gpt-oss:20b: pass 2026-09-20
  • qwen3.6:27b-mlx: pass 2026-09-20
  • 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
  • deepseek-r1:70b: pass 2026-09-19
  • gpt-oss:20b: pass 2026-09-19
  • qwen3.6:27b-mlx: pass 2026-09-18
  • deepseek-r1:70b: fail (style) 2026-09-18 — Step 1 is missing a rule label.
  • gpt-oss:20b: pass 2026-09-18
  • gpt-oss:20b: fail 2026-09-17 — Step 11 incorrectly combines the terms: 1/10 * ((5*x + 1)**2 + 1)**(-1/2) * (10*(5*x + 1)) simplifies to (5*x + 1)/sqrt((5*x + 1)**2 + 1), but the solution writes a fraction with an extra 10 in the denominator, leading to an algebraic mistake.
  • 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.