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Find the most general form of the antiderivative of f(x)= xe^(x^2).

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cspanutius | Student, Undergraduate | (Level 1) Salutatorian

Posted July 27, 2012 at 1:48 AM via web

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Find the most general form of the antiderivative of f(x)= xe^(x^2).

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted July 27, 2012 at 2:29 AM (Answer #1)

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Let `t = e^(x^2)`

Then `dt/dx = e^(x^2)*2x`

`dt = e^(x^2)*2xdx`

`f(x) = x*(e^(x^2))`

`intdt = int(e^(x^2)*2x)dx`

`intdt = 2*int(e^(x^2)*x)dx`

 

` int(e^(x^2)*x)dx`      = `(1/2)*intdt`

     ` intf(x)dx `     = `(1/2)(t)+C`

                         = (1/2)(e^(x^2))+C

 

So antiderivative f(x) = `(1/2)(e^(x^2))+C` where C is a constant.

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lfryerda | High School Teacher | (Level 2) Educator

Posted July 27, 2012 at 2:59 AM (Answer #2)

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To solve the integral `int xe^{x^2}dx` consider the substitution `u=x^2`.  Then `du=2xdx` which means the integral becomes

`1/2 int e^udu`

`=1/2 e^u + C`

`=1/2 e^x^2 +C`

If you have two functions multiplied together like `x` and `e^{x^2}` , where the derivative of the argument of the one function `(d/{dx}(x^2)=2x)`  is the other function, then we can always make the substitution which makes the integral easier to solve.

 

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