If the main reason for offence is the idea of a triune Godhead as opposed to a unitary one , then you are looking at it from the wrong angle, which may be the only way you as a Muslim have been shown to see it. Can't blame you for that. You associate the belief in the Trinity as worship of three persons ...this is not the case, it does not mean that. There is only one God, there are no partners to God in the way you see them ..as three separate individuals. As a simply analogy take an apple cut into three, its still an apple but has three separate pieces.

There are many examples why a triune God makes more sense than a unitary God, if you read the scriptures that is, The Trinity provides a coherent understanding of God’s nature, the doctrine of the Trinity provides a clear explanation and theological basis upon which one can understand the human desire for love and community. Prior to creation, if Allah was seen as non-relational how could it be possible for Muslims to expect any kind of relationship with him. As an inherently, non-relational being, Allah would be incapable of providing a basis for human community. The Trinity provides an explanation for the human pursuit of love. Because the Trinity has existed for all eternity in a community of love, the human desire for love springs from mankind’s reflection of the divine. Without a Creator who possesses plural-unity, an expression of love would be impossible. The Trinity conveys the overwhelming brilliance of a loving God Who exists in a vibrant community of love.