In D&C 20: 28 we have, "Which Father, Son, and Holy Ghost are one God, infinite and eternal, without end.
Mosiah 15:1-5 has a discussion of how the Father and the Son are one God.  The resurrected Christ declares in  3 Ne 11:14 "I am the God of Israel, and the God of the whole earth", but later, 3 Ne 11:36 "The Father, and I, and the Holy Ghost are one." Yet He prays to and speaks of the Father as a distinct, separate being than Himself, as He did throughout the New Testament.

The LDS reconcile these apparent contradictions by understanding the unity of the Father, Son, and Holy Ghost differently than most Christian theologians and philosphers would have it. It is not understood to be an ineffably mysterious identity of being or substance. It is rather understood to be a perfect unity of mind, outlook, understanding, purpose, will, and power. There are no quarrels, no wrangling, no cross-purposes, no separate agendas (as, for instance, the Greek or Roman gods). The LDS also take note of John 17:20-23 where Jesus prayed that those who believed would also become "one, as thou, Father art in me and I in thee", which points to a different meaning of "one" than is usually understood in Christian theology.

In D&C 20: 28 we have

Which Father, Son, and Holy Ghost are one God, infinite and eternal, without end. Amen

Mosiah 15:1-5 has a discussion of how the Father and the Son are one God. The resurrected Christ declares in 3 Ne 11:14

...I am the God of Israel, and the God of the whole earth

but later in 3 Ne 11:36

The Father, and I, and the Holy Ghost are one.

Yet He prays to and speaks of the Father as a distinct, separate being than Himself, as He did throughout the New Testament.

The LDS reconcile these apparent contradictions by understanding the unity of the Father, Son, and Holy Ghost differently than most Christian theologians and philosophers would have it. It is not understood to be an ineffably mysterious identity of being or substance. It is rather understood to be a perfect unity of mind, outlook, understanding, purpose, will, and power. There are no quarrels, no wrangling, no cross-purposes, no separate agendas (as, for instance, the Greek or Roman gods).¹

The LDS also take note of John 17:20-23 where Jesus prayed that those who believed would also become "one, as thou, Father art in me and I in thee", which points to a different meaning of "one" than is usually understood in Christian theology.

_{1 Gospel topics: godhead}