# Which integration technique was used here?

1. Sep 20, 2015

### duarthiago

I've just found the following example on Piskunov:

$\int \frac{t^2 dt}{(t^2 + 2)^2}\\= \frac{1}{2}\int \frac{t d(t^2 +2)}{(t^2 + 2)^2}\\=-\frac{1}{2}\int t d(\frac{1}{t^2 + 2})\\=-\frac{1}{2}\frac{t}{t^2 + 2}+\int \frac{dt}{t^2 + 2}\\=-\frac{t}{2(t^2 + 2)} + \frac{1}{2 \sqrt{2}}arctan\frac{t}{\sqrt{2}}$

What technique is this? Apparently there is a substitution at the beginning, but I can't figure out what happens from second line onwards.

2. Sep 20, 2015

### Staff: Mentor

The substitution was w = t2 + 2, so dw = 2tdt
In later steps it appears that they did integration by parts, with u = t and dv = dt/(t2 + 2).

3. Sep 20, 2015

### duarthiago

Of course! I didn't even try to see an integration by parts there. Thank you!

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