I want to explain the god is unique with maths.First of all , eveybody knows the answer of zero plus zero (0).As you know 1 is the beginning of the numbers.1 doesn't need any number to exist ,so other numbers need 1 to exist.
everything that was created later called created.Now think both of these together.Cristians believe three gods.I will say something if you understand the example above well .You believe a god whose son is jesus ,and you also believe holly spirit. Jesus and holly spirit were created by the unique god. İt is too nonsense to say they are also gods.They are just presence created by the god.Somebody or something that were created are not god because of their genesis.To say they are gods , and also worshipping to them altough they were created like you are fully nonsense.Islam is the single truth religion.