Open shape
x022xx
A5 is the A power chord. Its notes are A and E. No third means no major or minor quality. Mute unused strings carefully.
x022xx
577xxx
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every A and E on the first 12 frets. The filled dots are the root, A. Build your own shape from any nearby group.
Other A chords
Other power chords