反対だ
The two opinions are opposite.
二つの意見は反対です
The two opinions are opposite to each other.
二つの意見は互いに反対です
The two opinions are completely opposite to each other.
二つの意見は完全に互いに反対です
The two opinions are completely opposite to each other from the start.
二つの意見は最初から完全に互いに反対です
The two opinions on how to use the budget are completely opposite to each other from the start.
二つの意見は予算の使い道が最初から完全に互いに反対です