Integral of \( \displaystyle \frac{e^{2 x + 1}}{e^{2 x + 1} + 1} \)
Problem 4.996 · medium
Find \( \displaystyle \int \frac{e^{2 x + 1}}{e^{2 x + 1} + 1} \, dx \). (Omit the constant of integration.)
- \[ \int \frac{e^{2 x + 1}}{e^{2 x + 1} + 1}\, dx \]integral algebraStart with the integral of the given function. Rewrite the numerator to facilitate substitution.✓ Proved
- \[ = \int \frac{2 e^{2 x + 1}}{2 e^{2 x + 1} + 2}\, dx \]algebraMultiply and divide by 2.✓ Proved
- \[ = \int \frac{e^{2 x + 1}}{e^{2 x + 1} + 1}\, dx \]simplifySimplify the expression.✓ Proved
- \[ = \int \frac{1}{e^{- 2 x - 1} + 1}\, dx \]algebra algebraDivide numerator and denominator by exp(2*x + 1). Rewrite 1/exp(2*x + 1) as exp(-2*x - 1).✓ Proved
- \[ = \int \frac{e^{2 x + 1}}{e^{2 x + 1} + 1}\, dx \]simplify algebra algebraReturn to the original form for easier integration. Prepare for substitution by identifying the derivative of the denominator. Isolate the derivative of the denominator.✓ Proved
- \[ = \frac{\ln{\left(e^{2 x + 1} + 1 \right)}}{2} \]antiderivativeIntegrate using the substitution u = exp(2*x + 1) + 1, du = 2*exp(2*x + 1) dx.✓ Proved
Answer \( \frac{\ln{\left(e^{2 x + 1} + 1 \right)}}{2} + C \)
✓ 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 exp(2*x + 1) + 1 = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where exp(2*x + 1) + 1 = 0 undefined where 2*exp(2*x + 1) + 2 = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where 2*exp(2*x + 1) + 2 = 0 undefined where exp(2*x + 1) + 1 = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | lines differ by the constant 1/2 undefined where exp(2*x + 1) + 1 = 0 undefined where exp(-2*x - 1) + 1 = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where exp(-2*x - 1) + 1 = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | lines differ by the constant -1/2 undefined where exp(-2*x - 1) + 1 = 0 undefined where exp(2*x + 1) + 1 = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where exp(2*x + 1) + 1 = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where exp(2*x + 1) + 1 = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where exp(2*x + 1) + 1 = 0 log is undefined for non-positive arguments |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 log is undefined for non-positive arguments |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated the stated antiderivative back to the integrand |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: fail (style) — The solution contains redundant and circular steps (e.g., steps 2-4 and 7) that do not adhere to the 'one thing per step' principle effectively, creating a confusing path. Specifically, step 7 reverts to the original integrand, making the preceding simplification steps (5-6) pointless and the subsequent steps (8-9) repetitive of steps 2-4.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-13qwen3.6:27b-mlx: fail (style) 2026-10-13 — The solution contains redundant and circular steps (e.g., steps 2-4 and 7) that do not adhere to the 'one thing per step' principle effectively, creating a confusing path. Specifically, step 7 reverts to the original integrand, making the preceding simplification steps (5-6) pointless and the subsequent steps (8-9) repetitive of steps 2-4.gpt-oss:20b: pass 2026-10-13qwen3.6:27b-mlx: fail (style) 2026-10-13 — The solution contains redundant and circular steps (e.g., steps 2-4 and 7) that do not adhere to the 'one change per step' principle effectively, as they merely shuffle terms without progressing the solution. Steps 5-6 are unnecessary detours that complicate the path to the answer.
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 2026-10-13 with SymPy 1.14.0.