Question 1208350
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You clearly have not stated the problem correctly; or else the problem is faulty.<br>
If x is any multiple of 3, then x^2+9 is not prime.<br>
If x is any odd integer, then x^2 is odd, so x^2+9 is even, so it is not prime.<br>
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To the student, who suggests in his "thank you" note that I didn't know what to do with his question....<br>
It is YOU who does not know what to do.  You posted a problem without the required context.<br>
Without any context, when you ask "is x^2+9 prime", the usual interpretation is that you are talking about prime numbers.<br>
If you had posted your problem to ask whether "x^2+9 is a prime polynomial", then you would have saved both of us some wasted time.<br>