#1
I am curious because i wrote a catchy line and wanted to know if all the chords were in the same key or not.
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#2
Post the tab and we'll tell you.

For the most part, if the tonality of the chords isn't obvious, you can judge it based on the intervals, and looking at what scale it follows and in what key. Figuring out such things requires you to learn your scales: after a while you can just figure it out by looking at the intervals. Sorry if I've worded this badly.
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#3
if you're using them exclusively, just see if all the root notes of the chords fall in the same key.
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#5
if the score has a key signature that will tell you .
if its just tab , number them on degrees of a scale so

|A5|C5|D5|E5|

would be I5 bIII5 IV5 and V5

then compare these degrees to the natural minor or major scales


major is: I II III IV V VI VII
natural minor I II bIII VI V bVI bVII you may find accidentals in there or perhaps the I chord is not in the 1st bar but these tips should help get you started
#6
Quote by ibanez1511
|A5|C5|D5|E5|

would be I5 bIII5 IV5 and V5


in A minor, sure. though you wouldn't use bIII in that case. it's just III, since the key is known to be A minor.

it could also be a vi I ii iii in C major.

a iv VI VII i in E minor.

a ii IV V vi in G major. unresolving, of course, assuming this is repetitive. not as likely, but certainly possible.

even a iii V vi vii in F major or a v VII i ii in D minor are possible, since power chords generally disregard the fifth as actually being in the key.

"how does one tell what key power chords are in?" the only good answer is "by using one's ear."
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