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int x cos xdx

xcosxdx \int x \cos x d x

Full solution

Q. xcosxdx \int x \cos x d x
  1. Choose uu and dvdv: We will use integration by parts to solve the integral of xcos(x)dxx \cos(x) \, dx. Integration by parts is given by the formula udv=uvvdu\int u \, dv = uv - \int v \, du, where uu and dvdv are parts of the integrand that we choose. We will let u=xu = x and dv=cos(x)dxdv = \cos(x) \, dx.
  2. Find dudu and vv: Differentiate uu to find dudu, and integrate dvdv to find vv. So, du=dxdu = dx and v=sin(x)v = \sin(x). We can now apply the integration by parts formula.
  3. Apply integration by parts: Substitute uu, vv, and dudu into the integration by parts formula to get xcos(x)dx=xsin(x)sin(x)dx\int x \cos(x) \, dx = x \sin(x) - \int\sin(x) \, dx.
  4. Integrate sin(x)\sin(x): Now we need to integrate sin(x)dx\int \sin(x) \, dx, which is a basic integral. The integral of sin(x)\sin(x) with respect to xx is cos(x)-\cos(x).
  5. Substitute sin(x)\sin(x) integral: Substitute the integral of sin(x)\sin(x) into the equation from the previous step to get xcos(x)dx=xsin(x)(cos(x))\int x \cos(x) \, dx = x \sin(x) - (-\cos(x)).
  6. Simplify the equation: Simplify the equation by distributing the negative sign to get xcos(x)dx=xsin(x)+cos(x)+C\int x \cos(x) \, dx = x \sin(x) + \cos(x) + C, where CC is the constant of integration.