Problem

Find all integers k such that the trinomial x2kx+12 can be factored over the integers.

Answer

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Answer

By checking integers, we can find that the integers that satisfy this condition are k=8,6,6,8, since (8)2=64, (6)2=36, 62=36, and 82=64, all of which are 48 more than a perfect square.

Steps

Step 1 :The trinomial can be factored over the integers if and only if the discriminant Δ=b24ac is a perfect square, where a,b,c are the coefficients of the quadratic equation.

Step 2 :In this case, a=1, b=k, and c=12. Thus, Δ=(k)24112=k248.

Step 3 :For Δ to be a perfect square, k248 must be a perfect square. This happens when k is an integer such that k2 is 48 more than a perfect square.

Step 4 :By checking integers, we can find that the integers that satisfy this condition are k=8,6,6,8, since (8)2=64, (6)2=36, 62=36, and 82=64, all of which are 48 more than a perfect square.

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