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Evaluate the integral.

int-6x4^(-4x)dx
Answer:

Evaluate the integral.\newline6x44xdx \int-6 x 4^{-4 x} d x \newlineAnswer:

Full solution

Q. Evaluate the integral.\newline6x44xdx \int-6 x 4^{-4 x} d x \newlineAnswer:
  1. Define Integral: Let's denote the integral we want to evaluate as II:I=6x44xdxI = \int -6x4^{-4x}\,dxTo solve this integral, we will use integration by parts, which states that udv=uvvdu\int u\, dv = uv - \int v\, du, where uu and dvdv are differentiable functions of xx. We need to choose uu and dvdv such that the resulting integral is easier to solve. Let's choose:u=6xu = -6x (which means du=6dxdu = -6\, dx)dv=44xdxdv = 4^{-4x}\,dx (which means we need to find udv=uvvdu\int u\, dv = uv - \int v\, du00)To find udv=uvvdu\int u\, dv = uv - \int v\, du00, we need to integrate dvdv. Since udv=uvvdu\int u\, dv = uv - \int v\, du33 is an exponential function, we can use the fact that udv=uvvdu\int u\, dv = uv - \int v\, du44 when udv=uvvdu\int u\, dv = uv - \int v\, du55 and udv=uvvdu\int u\, dv = uv - \int v\, du66. In our case, udv=uvvdu\int u\, dv = uv - \int v\, du77 and udv=uvvdu\int u\, dv = uv - \int v\, du88, so udv=uvvdu\int u\, dv = uv - \int v\, du99.
  2. Integration by Parts: Now we integrate dvdv to find vv:
    v=4(4x)dxv = \int 4^{(-4x)}dx
    Using the formula for integrating an exponential function with a linear exponent, we get:
    v=4(4x)(4ln(4))v = \frac{4^{(-4x)}}{(-4\ln(4))}
    We can simplify this by multiplying the numerator and denominator by 1-1:
    v=4(4x)4ln(4)v = -\frac{4^{(-4x)}}{4\ln(4)}
  3. Choose uu and dvdv: Now that we have uu and vv, we can apply the integration by parts formula:\newlineI=uvvduI = uv - \int v du\newlineSubstituting uu, dudu, and vv into the formula, we get:\newlineI=6x(44x/(4ln(4)))(44x/(4ln(4)))(6dx)I = -6x\left(-4^{-4x}/(4\ln(4))\right) - \int\left(-4^{-4x}/(4\ln(4))\right)(-6 dx)\newlineSimplifying the integral, we get:\newlineI=6x44x4ln(4)+64ln(4)44xdxI = \frac{6x4^{-4x}}{4\ln(4)} + \frac{6}{4\ln(4)}\int 4^{-4x}dx
  4. Find v: We have already integrated 44x4^{-4x} when finding v, so we can use that result here:\newlineI=6x44x4ln(4)+64ln(4)(44x4ln(4))I = \frac{6x4^{-4x}}{4\ln(4)} + \frac{6}{4\ln(4)}\left(-\frac{4^{-4x}}{4\ln(4)}\right)\newlineSimplifying the expression, we get:\newlineI=3x44x2ln(4)344x8ln(4)2I = \frac{3x4^{-4x}}{2\ln(4)} - \frac{3\cdot 4^{-4x}}{8\ln(4)^2}
  5. Apply Integration by Parts: Now we can combine the terms with a common base of 44x4^{-4x}:\newlineI=3x44x2ln(4)344x8ln(4)2I = \frac{3x4^{-4x}}{2\ln(4)} - \frac{3\cdot 4^{-4x}}{8\ln(4)^2}\newline$I = \(4\)^{\(-4\)x}\left(\frac{\(3\)x}{\(2\)\ln(\(4\))} - \frac{\(3\)}{\(8\)\ln(\(4\))^\(2\)}\right)
  6. Simplify Integral: Finally, we add the constant of integration \(C\) to our result:\(\newline\)\(I = 4^{-4x}\left(\frac{3x}{2\ln(4)} - \frac{3}{8\ln(4)^2}\right) + C\)\(\newline\)This is the indefinite integral of the given function.

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