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)#