Note also the other comments I wrote:
With your recent edits and your sentence "The 1 God, YHWH, uses the singular masculine personal pronoun to describe Himself. So do the 3 persons of the trinity" I think you have the core of a good question here. But that core really doesn't have anything to do with the mathematical question you're wrapping around it. No Trinitarian ever said "1person+1person+1person=1person". Trinitarians are even extremely reluctant to use any addition or addition related notation when referring to the persons because of the doctrine of Divine Simplicity (God has no p…