What is the appropriate sentence? (Maybe something else?)
- They are both equal to each other.
- They both equal to each other.
NB: I'm not a native English speaker.
Of the two sentences you give They are both equal to each other is grammatical and They both equal to each other is not. "equal" in "equal to" is an adjective, so sentence 2 lacks a verb.
We can use equal as a verb, this would give the sentence They both equal each other.
They are both equal to each other and They both equal each other are grammatical and they express the same thing.
As others have noted there is redundancy in the above sentences, unless there is room for confusion a more concise sentence is preferable. - However without knowing more about context I would not state that sentence 1 is wrong.
Avoiding the redundancy is bad if there is room for confusion. For example if you are trying to make the following point; "Since a equals b we know that they both equal each other."
Q1. Are both of these equal? can also be framed as Are both of these same? "BOTH" = "EACH OTHER", and these are creating redundancy, thus, using either of them is sufficient.
Since the question is creating ambiguity about the subject, let us clarify about the subject which is being questioned. And that will lead to following questions...
Are both of these numbers equal? OR Are both of these objects same?
A1. Both of these/them are equal. OR Both of these/them are same.
OR to be concise
A1. Both are equal. OR Both are same.
Q2. Coming to next sentence of yours, this has no verb, so let us introduce a verb:
Question format: Are they both equal? OR Are they equal to each other?
Answer format: They both are equal. OR They are equal to each other.
Remember that BOTH = EACH OTHER and both together in a sentence creates unnecessary redundancy.
Neither.
You just say They are equal.
You do see sentences such as you quote used in practice. However, they contain redundant text.
Equality implies commutativity. That is, equality works both ways so you don't have to say it.
Neither of your sentences are correct actually.
They are equal
or They are equal to each other are two right forms of your relevant sentence.But my second sentence expresses the same meaning to the first one,So the ending part(To each other) is quite unnecessary here.
Then The right sentence is- They are equal.