Wolfram-Alpha is available for Android Devices, a search-oriented mathematics and aims to answer our questions directly and with a variety of data, graphs and tables.
For difficult questions, this search can be considered the best friend of all self-respecting nerd as well as stupid questions we can try yahoo answers and everything else, we always have to google.
While he needs evolve enough to reach the level he promised when he was born, more than once helped me with a comprehensive did not understand or it has shown a rapid and graphic doubt the issue that might happen.
So I think it is a great tool to have in your pocket, next to the wikipedia and some other little program “for nerds”. Believe me, the more you learn to use more will fall in love with this powerful search engine. And if you do not believe me, take a look at these examples of its potential.