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Evaluate the integral.

int2x^(2)e^(4x)dx
Answer:

Evaluate the integral.\newline2x2e4xdx \int 2 x^{2} e^{4 x} d x \newlineAnswer:

Full solution

Q. Evaluate the integral.\newline2x2e4xdx \int 2 x^{2} e^{4 x} d x \newlineAnswer:
  1. Identify Integral: Let's start by identifying the integral we need to evaluate:\newlineI=2x2e4xdxI = \int 2x^2e^{4x}\,dx\newlineThis integral suggests the use of integration by parts, where we let one part be differentiated and the other be integrated. We can choose u=x2u = x^2 and dv=2e4xdxdv = 2e^{4x}\,dx.
  2. Choose uu and dvdv: Now we need to find dudu and vv. Differentiating uu gives us du=2xdxdu = 2x\,dx, and integrating dvdv gives us v=(12)e4xv = \left(\frac{1}{2}\right)e^{4x} (since the integral of eaxe^{ax} is (1a)eax\left(\frac{1}{a}\right)e^{ax}).
  3. Find du and v: Applying the integration by parts formula, udv=uvvdu\int u\,dv = uv - \int v\,du, we get:\newlineI=uvvduI = uv - \int v\,du\newlineI=x2(12)e4x(12)e4x2xdxI = x^2 \cdot \left(\frac{1}{2}\right)e^{4x} - \int\left(\frac{1}{2}\right)e^{4x} \cdot 2x\,dx
  4. Apply Integration by Parts: Simplify the integral:\newlineI=12x2e4xxe4xdxI = \frac{1}{2}x^2e^{4x} - \int xe^{4x}\,dx\newlineNow we need to apply integration by parts again to the remaining integral, xe4xdx\int xe^{4x}\,dx. This time, let's choose u=xu = x and dv=e4xdxdv = e^{4x}\,dx.
  5. Simplify Integral: Differentiating uu gives us du=dxdu = dx, and integrating dvdv gives us v=14e4xv = \frac{1}{4}e^{4x}.
  6. Apply Integration by Parts Again: Applying the integration by parts formula again, we get:\newlineI=12x2e4x(x14e4x14e4xdx)I = \frac{1}{2}x^2e^{4x} - \left(x \cdot \frac{1}{4}e^{4x} - \int \frac{1}{4}e^{4x}\,dx\right)
  7. Simplify Integral: Simplify the integral and calculate the last integral:\newlineI=12x2e4x14xe4x+14×14e4xI = \frac{1}{2}x^2e^{4x} - \frac{1}{4}xe^{4x} + \frac{1}{4} \times \frac{1}{4}e^{4x}\newlineI=12x2e4x14xe4x+116e4xI = \frac{1}{2}x^2e^{4x} - \frac{1}{4}xe^{4x} + \frac{1}{16}e^{4x}
  8. Calculate Last Integral: Finally, we add the constant of integration CC to our result:\newlineI=(12)x2e(4x)(14)xe(4x)+(116)e(4x)+CI = \left(\frac{1}{2}\right)x^2e^{(4x)} - \left(\frac{1}{4}\right)xe^{(4x)} + \left(\frac{1}{16}\right)e^{(4x)} + C