# How to tell Mathematica to make assumptions? [duplicate]

Say I want to integrate 1/(x^2+a^2) and I want Mathematica to know that $a>0$. What would be the command? Something like:

Integrate[1/(x^2+a^2), {x, 0, 1}, {a > 0}]


Or, if I want to compute the limit of $\sin(xy)/(xy)$ as $(x,y)\to (0,0)$, $x,y$ reals, what would be the command?

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## marked as duplicate by Artes, Sjoerd C. de Vries, whuber, Michael E2, Oleksandr R.May 17 '13 at 2:58

Check the Assumptions options and check the examples in the Integrate documentation page. –  Szabolcs May 16 '13 at 19:49
Here's from the help file for Integrate: Integrate[x^n, {x, 0, 1}, Assumptions -> n > 0]. Maybe the help file would be helpful? –  bill s May 16 '13 at 20:07
As i know, there should be a command which is Assuming as follows,
Assuming[a > 0, Integrate[1/(x^2+a^2) ,{x,0,1}]]