For describing relation between mathematics & music ,If I say ancient theories ,I guess there are many disagreements to describe that they are just theories without applicability;
Therefore I prefer to describe application theories then I'll say ancient theories;We know music composed of harmony, melody and rhythm;
at first,For making a piece you must select scale,
If you take all 12 notes (the chromatic scale) and arrange them around a circle you produce a clock -like image; that is important for describing this topic.
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so, you have a seven-angles;
Move one of these angels, what happened?
Seven-angles turned around circle's center and makes a new scale!
Repeat this pattern for making any scale, you can't make mistake with this pattern,
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Many concepts in music can display as shapes and angles,
Think!
But why we have 12 tones in octave?
It has mathematical reason, too.