Integral of \( \displaystyle \sin{\left(2 x \right)} \cos{\left(2 x \right)} \)
Problem 4.561 · medium
Find \( \displaystyle \int \sin{\left(2 x \right)} \cos{\left(2 x \right)} \, dx \). (Omit the constant of integration.)
- \[ \int \sin{\left(2 x \right)} \cos{\left(2 x \right)}\, dx \]integralStart with the integral of the given function.✓ Proved
- \[ = \int \frac{\sin{\left(4 x \right)}}{2}\, dx \]trig-identityUse the double angle identity sin(2u) = 2sin(u)cos(u) with u = 2x.✓ Proved
- \[ = \frac{\int \sin{\left(4 x \right)}\, dx}{2} \]linearityFactor out the constant 1/2.✓ Proved
- \[ = - \frac{\cos{\left(4 x \right)}}{8} \]antiderivativeIntegrate sin(4*x) to get -cos(4*x)/4 and multiply by 1/2.✓ Proved
Answer \( \frac{\sin^{2}{\left(2 x \right)}}{4} + C \)
✓ 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 | lines differ by the constant 1/8 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: lines differ by the constant -1/8 |
| 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: pass
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07gpt-oss:20b: pass 2026-10-07
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 2026-10-07 with SymPy 1.14.0.