Limit of \( \displaystyle \frac{3 x}{\sqrt{\left(3 x - 1\right)^{2} + 4}} \) as \( x \to \infty \)
Problem 1.465 · medium
Evaluate \( \displaystyle \lim_{x \to \infty} \frac{3 x}{\sqrt{\left(3 x - 1\right)^{2} + 4}} \).
- \[ \lim_{x \to \infty}\left(\frac{3 x}{\sqrt{\left(3 x - 1\right)^{2} + 4}}\right) \]limitStart with the original limit expression.✓ Proved
- \[ = \lim_{x \to \infty}\left(\frac{3 x}{\sqrt{9 x^{2} - 6 x + 5}}\right) \]algebra simplifyExpand the squared term inside the square root. Combine the constant terms inside the square root.✓ Proved
- \[ = \lim_{x \to \infty}\left(\frac{3}{\sqrt{\frac{9 x^{2} - 6 x + 5}{x^{2}}}}\right) \]rewrite limit-lawDivide the numerator and denominator by x (noting x > 0). Apply the limit law for the quotient of two functions.✓ Proved
- \[ = \lim_{x \to \infty}\left(\frac{3}{\sqrt{9 - \frac{6}{x} + \frac{5}{x^{2}}}}\right) \]simplifyDistribute the division by x^2 inside the square root.✓ Proved
- \[ = \lim_{x \to \infty} 1 \]infinity simplifyEvaluate the terms involving 1/x as x approaches infinity. Simplify the expression inside the limit.✓ Proved
- \[ = 1 \]limitEvaluate the final numerical value.✓ Proved
Answer \( 1 \)
✓ 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 undefined where (3*x - 1)**2 + 4 = 0 undefined where 9*x**2 - 6*x + 5 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 9*x**2 - 6*x + 5 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 9*x**2 - 6*x + 5 = 0 undefined where x = 0 undefined where (9*x**2 - 6*x + 5)/x**2 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where (9*x**2 - 6*x + 5)/x**2 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where (9*x**2 - 6*x + 5)/x**2 = 0 undefined where 9 - 6/x + 5/x**2 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where x = 0 undefined where 9 - 6/x + 5/x**2 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy took the limit from both sides and got the stated value |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly applies algebraic simplification and limit laws to evaluate the limit at infinity. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09 — The solution correctly applies algebraic simplification and limit laws to evaluate the limit at infinity. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.gpt-oss:20b: pass 2026-10-09qwen3.6:27b-mlx: pass 2026-10-09 — The solution correctly applies algebraic manipulations and limit laws to evaluate the limit. Each step changes only one aspect of the expression and uses valid labels from the fixed vocabulary.
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 2026-10-09 with SymPy 1.14.0.