Thread: Integral

Hello


How do you integrate this, Integral (5x/3)*e^-x/3


Thank you

Hello,

Originally Posted by mladen

Hello


How do you integrate this, Integral (5x/3)*e^-x/3


Thank you

When you have the integral of a product involving a polynomial (5x/3) and a "basic" exponential (e^-x/3), think "Integration by parts".

Take and

You refer to partiall integration?


F(x)g(x) - integral F(x)g(x)´


Så I should set F(x) = 5x/3 and g(x) = e^-x/3 ?

thank you

Originally Posted by mladen

You refer to partiall integration?


F(x)g(x) - integral F(x)g(x)´


Så I should set F(x) = 5x/3 and g(x) = e^-x/3 ?

thank you

Hm...

This is not the formula, but it looks like...



And take and






Edit : your writing is confusing me... What is the original integral with f and g for you ?

The original integral is "integral 5x/3*e^-x/3"


I set g(x) = e^-x/3
And f(x) = 5x/3


then used the formula

F(x)g(x) - integral F(x)g(x)´

Originally Posted by mladen

The original integral is "integral 5x/3*e^-x/3"


I set g(x) = e^-x/3
And f(x) = 5x/3


then used the formula

F(x)g(x) - integral F(x)g(x)´

Ok that's it

Set f(x)=e^-x/3
And g(x)=5x/3

Because g will be differentiated. Since the derivative of an exponential is in most case the same, it's not really useful to set g(x)=e^-x/3
Whereas if you differentiate a polynomial (5x/3), you will soon get to a constant.
Do you understand ?

Yes I think I understand it now. Thanks alot =)