Derivative of \( \displaystyle \sqrt{\left(x + 1\right)^{2} + 1} \)
Problem 2.956 · medium
Differentiate \( \displaystyle f(x) = \sqrt{\left(x + 1\right)^{2} + 1} \).
- \[ \frac{d}{d x} \sqrt{\left(x + 1\right)^{2} + 1} \]derivative rewriteStart with the derivative of the function. Rewrite the square root as a fractional power.✓ Proved
- \[ = \frac{\frac{d}{d x} \left(\left(x + 1\right)^{2} + 1\right)}{2 \sqrt{\left(x + 1\right)^{2} + 1}} \]chainApply the chain rule.✓ Proved
- \[ = \frac{\frac{d}{d x} 1 + \frac{d}{d x} \left(x + 1\right)^{2}}{2 \sqrt{\left(x + 1\right)^{2} + 1}} \]sumDifferentiate the sum inside the parentheses.✓ Proved
- \[ = \frac{\left(2 x + 2\right) \frac{d}{d x} \left(x + 1\right)}{2 \sqrt{\left(x + 1\right)^{2} + 1}} \]powerApply the power rule to (x + 1)**2.✓ Proved
- \[ = \frac{2 x + 2}{2 \sqrt{\left(x + 1\right)^{2} + 1}} \]derivative simplifyDifferentiate the inner term (x + 1). Simplify the expression.✓ Proved
- \[ = \frac{x + 1}{\sqrt{\left(x + 1\right)^{2} + 1}} \]simplify simplifyCancel the 2 and 1/2. Rewrite with a positive exponent.✓ Proved
Answer \( \frac{x + 1}{\sqrt{\left(x + 1\right)^{2} + 1}} \)
✓ 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
| 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 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 undefined where (x + 1)**2 + 1 = 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-09-27gpt-oss:20b: pass 2026-09-27qwen3.6:27b-mlx: pass 2026-09-27gpt-oss:20b: pass 2026-09-27
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 2026-09-27 with SymPy 1.14.0.