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Evaluate the integral.

int4x^(3)sin(4x)dx
Answer:

Evaluate the integral.\newline4x3sin(4x)dx \int 4 x^{3} \sin (4 x) d x \newlineAnswer:

Full solution

Q. Evaluate the integral.\newline4x3sin(4x)dx \int 4 x^{3} \sin (4 x) d x \newlineAnswer:
  1. Identify Integral: Identify the integral to be solved.\newlineWe need to evaluate the integral of 4x3sin(4x)4x^3\sin(4x) with respect to xx, which is written as 4x3sin(4x)dx\int 4x^3\sin(4x)\,dx.
  2. Use Integration by Parts: Use integration by parts. 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. We need to choose uu and dvdv such that the resulting integral is simpler. Let's choose u=x3u = x^3 (which will simplify when differentiated) and dv=4sin(4x)dxdv = 4\sin(4x)\,dx (which will integrate easily).
  3. Differentiate and Integrate: Differentiate uu and integrate dvdv.\newlineDifferentiating u=x3u = x^3 gives us du=3x2dxdu = 3x^2dx.\newlineIntegrating dv=4sin(4x)dxdv = 4\sin(4x)dx gives us v=cos(4x)v = -\cos(4x).
  4. Apply Integration by Parts: Apply the integration by parts formula.\newlineNow we apply the integration by parts formula:\newline4x3sin(4x)dx=uvvdu\int 4x^3\sin(4x)\,dx = uv - \int v\,du\newline=x3(cos(4x))(cos(4x))(3x2)dx= x^3(-\cos(4x)) - \int(-\cos(4x))(3x^2)\,dx\newline=x3cos(4x)+3x2cos(4x)dx= -x^3\cos(4x) + 3\int x^2\cos(4x)\,dx
  5. Apply Integration by Parts Again: Apply integration by parts again to the remaining integral.\newlineWe need to apply integration by parts to the integral 3x2cos(4x)dx3\int x^2\cos(4x)\,dx. Let's choose u=x2u = x^2 and dv=3cos(4x)dxdv = 3\cos(4x)\,dx.\newlineDifferentiating u=x2u = x^2 gives us du=2xdxdu = 2x\,dx.\newlineIntegrating dv=3cos(4x)dxdv = 3\cos(4x)\,dx gives us v=34sin(4x)v = \frac{3}{4}\sin(4x).
  6. Apply Integration by Parts Formula: Apply the integration by parts formula to the new integral.\newlineNow we apply the integration by parts formula to the new integral:\newline3x2cos(4x)dx=uvvdu3\int x^2\cos(4x)\,dx = uv - \int v\,du\newline=x2(34)sin(4x)(34)sin(4x)(2x)dx= x^2(\frac{3}{4})\sin(4x) - \int(\frac{3}{4})\sin(4x)(2x)\,dx\newline=(34)x2sin(4x)(32)xsin(4x)dx= (\frac{3}{4})x^2\sin(4x) - (\frac{3}{2})\int x\sin(4x)\,dx
  7. Apply Integration by Parts One More Time: Apply integration by parts one more time to the remaining integral.\newlineWe need to apply integration by parts to the integral (32)xsin(4x)dx(\frac{3}{2})\int x\sin(4x)\,dx. Let's choose u=xu = x and dv=(32)sin(4x)dxdv = (\frac{3}{2})\sin(4x)\,dx.\newlineDifferentiating u=xu = x gives us du=dxdu = dx.\newlineIntegrating dv=(32)sin(4x)dxdv = (\frac{3}{2})\sin(4x)\,dx gives us v=(38)cos(4x)v = -(\frac{3}{8})\cos(4x).
  8. Apply Integration by Parts Formula: Apply the integration by parts formula to the final integral.\newlineNow we apply the integration by parts formula to the final integral:\newline(32)xsin(4x)dx=uvvdu(\frac{3}{2})\int x\sin(4x)\,dx = uv - \int v\,du\newline=x(38)cos(4x)(38)cos(4x)dx= x(-\frac{3}{8})\cos(4x) - \int(-\frac{3}{8})\cos(4x)\,dx\newline=(38)xcos(4x)+(38)(14)sin(4x)= -(\frac{3}{8})x\cos(4x) + (\frac{3}{8})(\frac{1}{4})\sin(4x)\newline=(38)xcos(4x)+(332)sin(4x)= -(\frac{3}{8})x\cos(4x) + (\frac{3}{32})\sin(4x)
  9. Combine All Parts: Combine all parts to get the final answer.\newlineCombining all parts, we get:\newline4x3sin(4x)dx=x3cos(4x)+34x2sin(4x)38xcos(4x)+332sin(4x)+C\int 4x^3\sin(4x)\,dx = -x^3\cos(4x) + \frac{3}{4}x^2\sin(4x) - \frac{3}{8}x\cos(4x) + \frac{3}{32}\sin(4x) + C\newlinewhere CC is the constant of integration.