Integral of \( \displaystyle \cos^{3}{\left(x \right)} \)
Problem 4.358 · easy
Find \( \displaystyle \int \cos^{3}{\left(x \right)} \, dx \). (Omit the constant of integration.)
- \[ \int \cos^{3}{\left(x \right)}\, dx \]integral algebraStart with the integral of the function. Rewrite the power as a product.✓ Proved
- \[ = \int \left(1 - \sin^{2}{\left(x \right)}\right) \cos{\left(x \right)}\, dx \]trig-identityUse the identity cos(x)**2 = 1 - sin(x)**2.✓ Proved
- \[ = - \int \sin^{2}{\left(x \right)} \cos{\left(x \right)}\, dx + \int \cos{\left(x \right)}\, dx \]linearityDistribute the cos(x) and split the integral.✓ Proved
- \[ = \sin{\left(x \right)} - \int \sin^{2}{\left(x \right)} \cos{\left(x \right)}\, dx \]antiderivative substitution algebraIntegrate the first term. Express the integrand in terms of the derivative of sin(x). The derivative of sin(x) is cos(x).✓ Proved
- \[ = - \frac{\sin^{3}{\left(x \right)}}{3} + \sin{\left(x \right)} \]antiderivativeIntegrate the remaining term using the power rule for substitution.✓ Proved
Answer \( - \frac{\sin^{3}{\left(x \right)}}{3} + \sin{\left(x \right)} + C \)
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. The reviewers disagree about how one step is explained; every verdict is in the receipt.
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 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 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 |
| 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 differentiated the stated antiderivative back to the integrand |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: fail (error) — Step 7 is mathematically incorrect; it claims that Integral(sin(x)**2 * sin(x).diff(x), x) equals Integral(sin(x)**2 * cos(x), x), which is false because the former evaluates to sin(x)**3/3 while the latter is an unevaluated integral. Additionally, Step 4 applies two rules (distribution and linearity of integration) simultaneously.
Every verdict on record (4)
qwen3.6:27b-mlx: fail (error) 2026-10-05 — Step 7 is mathematically incorrect; it claims that Integral(sin(x)**2 * sin(x).diff(x), x) equals Integral(sin(x)**2 * cos(x), x), which is false because the former evaluates to sin(x)**3/3 while the latter is an unevaluated integral. Additionally, Step 4 applies two rules (distribution and linearity of integration) simultaneously.gpt-oss:20b: pass 2026-10-05qwen3.6:27b-mlx: pass 2026-10-05gpt-oss:20b: pass 2026-10-05
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 2026-10-05 with SymPy 1.14.0.