The Father is God
2Pe_1:17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
The Son is God
Psa 78:35 And they remembered that God was their rock, and the high God their redeemer.
1Co 10:2 And were all baptized unto Moses in the cloud and in the sea;
1Co 10:3 And did all eat the same spiritual meat;
1Co 10:4 And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.
Jesus is God because the OT says Israel's Rock was God and Christ was that same Rock.
Holy Spirit is God
Act 5:1 But a certain man named Ananias, with Sapphira his wife, sold a possession,
Act 5:2 And kept back part of the price, his wife also being privy to it, and brought a certain part, and laid it at the apostles' feet.
Act 5:3 But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land?
Act 5:4 Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God.
Here lying to the Holy Spirit is called lying to God.
To believe in the Trinity is to believe these three things are true, that the Father, Son and Holy Spirit are each God in their own right and work together as One.
The Trinity is found in these verses, some from the OT!
2Co 13:14 May the grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all. Amen.
Lord Jesus Christ, God (the Father), the Holy Spirit, the Trinity!
Isaiah 48:16-17 “Come near to Me, hear this: I have not spoken in secret from the beginning; from the time that it was, I was there. And now the Lord God and His Spirit have sent Me. Thus says the Lord, your redeemer”
Here is a person speaking who was there from the beginning, and says he is "the Lord, your redeemer", and He mentions "the Lord God and His Spirit" that is the Trinity!
Isaiah 42:1 “Behold! My Servant whom I uphold, My Elect One in whom My soul delights! I have put My Spirit upon Him; He will bring forth justice to the Gentiles.”
Here God (the Father) speaks of his elect servant (Jesus) and His Spirit which is the Holy Spirit, and that is the Trinity!