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Evaluate the integral.

int-5x cos(5x+5)dx
Answer:

Evaluate the integral.\newline5xcos(5x+5)dx \int-5 x \cos (5 x+5) d x \newlineAnswer:

Full solution

Q. Evaluate the integral.\newline5xcos(5x+5)dx \int-5 x \cos (5 x+5) d x \newlineAnswer:
  1. Identify Integral: Let's first identify the integral we need to evaluate:\newlineI=5xcos(5x+5)dxI = \int -5x \cos(5x+5) \, dx\newlineWe can use integration by parts, which states that udv=uvvdu\int u \, dv = uv - \int v \, du, where uu is a function of xx, and dvdv is the differential of another function of xx.\newlineLet's choose u=5xu = -5x (which will be differentiated) and dv=cos(5x+5)dxdv = \cos(5x+5) \, dx (which will be integrated).
  2. Choose uu and dvdv: Differentiate uu with respect to xx to find dudu:
    u=5xu = -5x
    du=5dxdu = -5 \, dx
  3. Differentiate uu: Integrate dvdv to find vv:
    dv=cos(5x+5)dxdv = \cos(5x+5) \, dx
    To integrate dvdv, we need to use the substitution method. Let w=5x+5w = 5x+5, then dw=5dxdw = 5 \, dx, which means dx=dw5dx = \frac{dw}{5}.
    v=cos(w)dw5v = \int \cos(w) \, \frac{dw}{5}
    v=15sin(w)+Cv = \frac{1}{5}\sin(w) + C
    Since w=5x+5w = 5x+5, we substitute back to get vv in terms of dvdv22:
    dvdv33
  4. Integrate dv: Now apply the integration by parts formula:\newlineI=uvvduI = uv - \int v du\newlineI=(5x)(15)sin(5x+5)(15)sin(5x+5)(5)dxI = (-5x)(\frac{1}{5})\sin(5x+5) - \int (\frac{1}{5})\sin(5x+5)(-5) dx\newlineSimplify the expression:\newlineI=xsin(5x+5)+sin(5x+5)dxI = -x \sin(5x+5) + \int \sin(5x+5) dx
  5. Apply Integration by Parts: Now we need to integrate sin(5x+5)dx\int \sin(5x+5) \, dx. We will use the substitution method again with w=5x+5w = 5x+5, dw=5dxdw = 5 \, dx, and dx=dw5dx = \frac{dw}{5}.\newlineI=xsin(5x+5)+15sin(w)dwI = -x \sin(5x+5) + \frac{1}{5}\int\sin(w) \, dw\newlineIntegrate sin(w)\sin(w) with respect to ww:\newlineI=xsin(5x+5)+15(cos(w))+CI = -x \sin(5x+5) + \frac{1}{5}(-\cos(w)) + C\newlineSubstitute back w=5x+5w = 5x+5 to get the integral in terms of xx:\newlinew=5x+5w = 5x+500