SOLUTION: Find the number of positive integers n, {{{1<=n<=1000}}}, for which the polynomial {{{x^2 + x - n}}} can be factored as the product of two linear factors with integer coefficients.

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: Find the number of positive integers n, {{{1<=n<=1000}}}, for which the polynomial {{{x^2 + x - n}}} can be factored as the product of two linear factors with integer coefficients.      Log On


   



Question 1157075: Find the number of positive integers n, 1%3C=n%3C=1000, for which the polynomial x%5E2+%2B+x+-+n can be factored as the product of two linear factors with integer coefficients.
Answer by ikleyn(52810) About Me  (Show Source):
You can put this solution on YOUR website!
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The polynomial of this kind is factorable IF and ONLY IF  " n " is the product of two consecutive integer numbers n = m*(m+1).


Then  x^2 + x -n = (x+m)*(x-(m+1)).


So, you should determine the number of all such positive n's  under the condition  1 <= m*(m+1) <= 1000.


Notice that " m " can be positive and negative, as well.


So, you need to find the number of solutions to this compound inequality

        1 <= m*(m+1) <= 1000.


The solutions are   -32 <= m <= 31; but you should reject negative m's and m = 0.

So, the number of such positive n's is 31.

ANSWER. 31.


Solved.