We need to find the correct solution for the integral $\int x^2 \sin x \, dx$.

AnalysisIntegrationIntegration by PartsDefinite Integral
2025/5/10

1. Problem Description

We need to find the correct solution for the integral x2sinxdx\int x^2 \sin x \, dx.

2. Solution Steps

We will use integration by parts twice. The integration by parts formula is:
udv=uvvdu\int u \, dv = uv - \int v \, du
First, let u=x2u = x^2 and dv=sinxdxdv = \sin x \, dx. Then du=2xdxdu = 2x \, dx and v=cosxv = -\cos x. Applying integration by parts:
x2sinxdx=x2(cosx)(cosx)(2x)dx=x2cosx+2xcosxdx\int x^2 \sin x \, dx = x^2(-\cos x) - \int (-\cos x)(2x) \, dx = -x^2 \cos x + 2 \int x \cos x \, dx
Now, we need to evaluate xcosxdx\int x \cos x \, dx. We'll use integration by parts again.
Let u=xu = x and dv=cosxdxdv = \cos x \, dx. Then du=dxdu = dx and v=sinxv = \sin x. Applying integration by parts:
xcosxdx=xsinxsinxdx=xsinx(cosx)=xsinx+cosx\int x \cos x \, dx = x \sin x - \int \sin x \, dx = x \sin x - (-\cos x) = x \sin x + \cos x
Substituting this back into the original integral:
x2sinxdx=x2cosx+2(xsinx+cosx)+C=x2cosx+2xsinx+2cosx+C\int x^2 \sin x \, dx = -x^2 \cos x + 2 (x \sin x + \cos x) + C = -x^2 \cos x + 2x \sin x + 2 \cos x + C

3. Final Answer

The correct solution is x2cosx+2xsinx+2cosx+C-x^2 \cos x + 2x \sin x + 2 \cos x + C. This matches option B.
Final Answer: Option B

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