What is #f(x) = int 3x^3-2x+xe^(x-2) dx# if #f(1) = 3 #?

1 Answer
Mar 27, 2017

#f(x)=3x^4/4 -2x^2/2+(x-1)e^(x-2)+13/4#

Explanation:

Let's first evaluate the indefinite integral:

#f(x)=int(3x^3-2x+xe^(x-2))dx#

#=int(3x^3)dx -int(2x)dx+int(xe^(x-2))dx#

#=3x^4/4 -2x^2/2+C+int(xe^(x-2))dx# where #C# is the constant of integration.

We can evaluate #int(xe^(x-2))dx# using integration by parts as follows:

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

Evaluating #int(xe^(x))dx#:
#int(xe^(x-2))dx = xe^x - int(e^x)dx#
#= xe^x - e^x +C#

Therefore, #int(xe^(x-2))dx = e^-2(xe^x - e^x)+C#
#=(x-1)e^(x-2)+C#

Therefore, the original integral is equal to:

#f(x)=3x^4/4 -2x^2/2+(x-1)e^(x-2)+C#

Plugging in #x=1#, we get:

#f(1)=3/4 -1+0+C =-1/4+C#

But #f(1)=3#

So, #3=-1/4+C => C=3+1/4=13/4#

Therefore,

#f(x)=3x^4/4 -2x^2/2+(x-1)e^(x-2)+13/4#