Romans 1:20>For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse.
God's nature can be seen through nature itself. In Jeremiah 1, there are creatures with multiple heads and one body. Who created such a being? The Trinity is not of pagan origin.
Other examples: The Universe consists of time, matter, space. All three distinct, but one in the universe. And there are trinities within that also. Time can be past, present, future. Matter can be solid, liquid, gas. Space can be length, width, height. There are many examples of trinities. My last and favorite is: Water can be hot, warm, cold and still remains H2O no matter what the temperature. Is it suprising that God's nature can be mind boggling? The only thing that's mind boggling is an idea of the serpant decieving Adam and Eve before God warns them not to eat of the tree. This logic of God is applied in Islam, seeing that they ignore the forewarnings of the Holy Bible of up and coming false revelations.
SubhanAllah and His only begotten Son Jesus Christ.