A Power Chord (5) (A5)
1+5
Notes in A Power Chord (5)
A (root)E
Inversions
Same notes as A Power Chord (5), with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
A in the bass
1st inversion
E in the bass (A5/E)
A Power Chord (5) is built from A and E.
Just a root and a fifth, no third at all. That makes it neither major nor minor, which is why rock guitar and simple piano left-hand parts lean on it so much. It sounds strong and neutral, and it leaves room for a singer or another instrument to decide the mood.