Limit of \( \displaystyle \frac{2 x + \left(2 x - 1\right)^{2} - 7}{2 x - 3} \) as \( x \to \frac{3}{2} \)
Problem 1.140 · medium
Evaluate \( \displaystyle \lim_{x \to \frac{3}{2}} \frac{2 x + \left(2 x - 1\right)^{2} - 7}{2 x - 3} \).
- \[ \lim_{x \to \frac{3}{2}^+}\left(\frac{2 x + \left(2 x - 1\right)^{2} - 7}{2 x - 3}\right) \]limitStarting with the limit of the function at x = 3/2.✓ Proved
- \[ = \lim_{x \to \frac{3}{2}^+}\left(\frac{4 x^{2} - 2 x - 6}{2 x - 3}\right) \]algebra simplify factorExpand the squared term. Combine like terms in the numerator. Factor out a 2 from the numerator.✓ Proved
- \[ = \lim_{x \to \frac{3}{2}^+}\left(\frac{\left(x + 1\right) \left(4 x - 6\right)}{2 x - 3}\right) \]factorFactor the quadratic expression in the numerator.✓ Proved
- \[ = \lim_{x \to \frac{3}{2}^+}\left(2 x + 2\right) \]cancel simplifyCancel the common factor (2*x - 3). Distribute the 2.✓ Proved
- \[ = 5 \]substitution algebra limitSubstitute x = 3/2 into the expression. Multiply 2 by 3/2. Final evaluation of the limit.✓ Proved
Answer \( 5 \)
✓ 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 - 3 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x - 3 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x - 3 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x - 3 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*x - 3 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 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 |
| 10 | ✓ 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 expands, factors, cancels, and substitutes to evaluate the limit. Each step applies a single rule and is labeled correctly.
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-04 — The solution correctly expands, factors, cancels, and substitutes to evaluate the limit. Each step applies a single rule and is labeled correctly.gpt-oss:20b: pass 2026-10-04qwen3.6:27b-mlx: pass 2026-10-04gpt-oss:20b: pass 2026-10-04
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 2026-10-04 with SymPy 1.14.0.