# Why is it hard to prove whether $\pi+e$ is an irrational number?

From this list I came to know that it is hard to conclude $\pi+e$ is an irrational? Can somebody discuss with reference "Why this is hard ?"

Is it still an open problem ? If yes it will be helpful to any student what kind ideas already used but ultimately failed to conclude this.

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According to mathworld, it's still an open problem: mathworld.wolfram.com/e.html –  Cocopuffs Jun 17 '12 at 6:39
The same think is asked in (a part of) this question: math.stackexchange.com/questions/28243/… –  Martin Sleziak Jun 17 '12 at 6:41
I don't think this is precisely a duplicate of the other question, as this one asks for references and discussion about why previous techniques are insufficient to resolve the problem. (I've edited the title to match.) This can be more illuminating than a simple yes/no answer, which is what the previous question received. –  Rahul Jun 17 '12 at 6:51
Why shouldn't it be hard? –  Qiaochu Yuan Jun 17 '12 at 7:32
@Qiaochu, I agree that the obvious answer to the stated question is "why not?", but negative results about what kinds of techniques cannot possibly work can still give much insight. For example, there are several results regarding what classes of proofs are insufficiently powerful to resolve P vs. NP. I've upvoted this question because I guess I'm hoping to learn something similar here. –  Rahul Jun 17 '12 at 8:01

"Why is this hard?" I think a different question would be "Why would it be easy?"

But there are some things that are known. It is known that $\pi$ and $e$ are transcendental. Thus $(x-\pi)(x-e) = x^2 - (e + \pi)x + e\pi$ cannot have rational coefficients. So at least one of $e + \pi$ and $e\pi$ is irrational. It's also known that at least one of $e \pi$ and $e^{\pi^2}$ is irrational (see, e.g., this post at MO).

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## protected by Asaf KaragilaJul 12 '13 at 1:02

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