How would you integrate (x^2)(e^(x-1))?

1 Answer
May 22, 2015

You would need to do a bit of integration by parts here.

lets first set f(x) = x^2 and g'(x) = e^(x-1)

and use u = f(x) and v = g(x)

then du = f'(x) dx and dv = g'(x)

and we use the integral by parts formula:

intudv = uv - intv du

Now let us get the values:

u = x^2 and v= e^(x-1)

du = 2x and dv= e^(x-1)

Thus:

int x^2e^(x-1) dx = x^2e^(x-1) - int 2xe^(x-1) dx

int x^2e^(x-1) dx = x^2e^(x-1) - 2int xe^(x-1) dx

now lets solve for color(red)(int xe^(x-1) dx)

color(red)(u = x) and color(red)(v=e^(x-1))

color(red)(du = 1) and color(red)(dv=e^(x-1))

Thus:

color(red)( int xe^(x-1) = xe^(x-1) - int 1e^(x-1)

which equals:

color(red)( int xe^(x-1) = xe^(x-1) - e^(x-1)

Now we can substitute that back into our first problem, and get:

int x^2e^(x-1) dx = x^2e^(x-1) - 2int xe^(x-1) dx

is equal to, int x^2e^(x-1) dx = x^2e^(x-1) - 2(xe^(x-1) - e^(x-1))

where we can simplify to:

int x^2e^(x-1) = e^(x-1)(x^2 - 2x + 2)