# Integration problem

#### Cameron.S

##### New member
Struggling to integrate the equation, pretty sure it can be done by integrating by parts but not sure how

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#### Dr.Peterson

##### Elite Member
You should be able to immediately integrate $$\displaystyle e^{-\frac{t}{T}}$$. That doesn't require parts, just a simple substitution, if that.

What you might want to do is first just to check the answer they give; in fact, that is really enough to answer the question. Differentiate the given function $$\displaystyle \phi(t)$$, and show that (a) the derivative is what you were given, and (b) $$\displaystyle \phi(0) = 0$$.

#### Cameron.S

##### New member
Thanks for the help, tried this method and I’m missing the 1 inside the brackets. Not sure how this can be found?

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#### Subhotosh Khan

##### Super Moderator
Staff member
Thanks for the help, tried this method and I’m missing the 1 inside the brackets. Not sure how this can be found?
Where did C go in your final step?

#### Dr.Peterson

##### Elite Member
You'll have to use the fact that $$\displaystyle \phi(0) = 0$$ to determine the value of C. You can't just call it 0, as you have.