you can't really power it off, as they are both the same device technically, you can however turn of the tablet screen to save power. To do this I recommend either using the app that came with it called screen lock. The other option is to add the power widget to the home screen(you can add widgets by tapping and holding on the home screen), the widget has an option to turn off the screen.
No matter which app you use, to turn back on the tablet screen all you have to do is press the menu button.
Hope this helps!
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