1 is not a prime number.
But the question "is it prime" has nothing to do with 5 and 3 or 5 and 1.
You cannot factor a prime polynomial. You'd have to use the quadratic formula.
The fact that you were able to factor it proves it isn't prime.
The test for prime is step 1. If it's prime, use the quadratic.
Remember the general quadratic polynomial is
To test for prime determine if
In this case the discriminant is
4900 is a perfect square, so the polynomial is not prime.
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