SOLUTION: For how many integers m is it true that x^2 −8+(4m)(x−2)^2 +(m^2)((x−2)^2) ≥0 for all real values of x? (A) 4 (B) 0 (C) 5 (D) 3 (E) 2

Algebra ->  Inequalities -> SOLUTION: For how many integers m is it true that x^2 −8+(4m)(x−2)^2 +(m^2)((x−2)^2) ≥0 for all real values of x? (A) 4 (B) 0 (C) 5 (D) 3 (E) 2      Log On


   



Question 1163110: For how many integers m is it true that x^2 −8+(4m)(x−2)^2 +(m^2)((x−2)^2) ≥0 for all real values of x?
(A) 4 (B) 0 (C) 5 (D) 3 (E) 2

Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
For a parabola with equation y=ax²+bx+c to have non-negative values for all
x, then except possibly for its vertex, it must be totally above the x-axis,
or possibly with only its vertex on the x-axis with the parabola tangent to
the x-axis at its vertex.  That is,

1. The parabola must open upward, i.e., its leading coefficient is positive.
2. It must have only one or no real zeros, i.e., its discriminant is 
non-positive.  That is, a > 0 and b²-4ac ≤ 0.

x%5E2-8%2B4m%28x-2%29%5E2%2Bm%5E2%28x-2%29%5E2+%3E=0

x%5E2-8%2B4m%28x%5E2-4x%2B4%29%2Bm%5E2%28x%5E2-4x%2B4%29+%3E=0

x%5E2-8%2B4mx%5E2-16mx%2B16m%2Bm%5E2x%5E2-4m%5E2x%2B4m%5E2+%3E=0

%28m%5E2%2B4m%2B1%29x%5E2-4%28m%5E2%2B4m%29x%2B4%28m%5E2%2B4m%29-8+%3E=0

Requiring that the leading coefficient must be positive:

m%5E2%2B4m%2B1%3E0

That represents a parabola opening upward. It has approximately zeros -3.7
and -0.3, thus for integer m,

matrix%281%2C3%2Cm+%3C=+-4%2C+or%2C+m+%3E=+0%29

Requiring that the discriminant be non-positive:

%28-4%28m%5E2%2B4m%29%29%5E2-4%28m%5E2%2B4m%2B1%29%284%28m%5E2%2B4m%29-8%29+%3C=+0

%28-4%28m%5E2%2B4m%29%29%5E2-4%28m%5E2%2B4m%2B1%29%284%28m%5E2%2B4m%29-8%29+%3C=+0

%28-4m%5E2-16m%29%5E2-4%28m%5E2%2B4m%2B1%29%284m%5E2%2B16m-8%29+%3C=+0

16m%5E4%2B128m%5E3%2B256m%5E2-16m%5E4-128m%5E3-240m%5E2%2B+64+m+%2B+32+%3C=+0

16m%5E2+%2B+64m+%2B+32%3C=0

Divide through by 16

m%5E2+%2B+4+m+%2B+2%3C=0

That is a parabola opening upward, and has approximate zeros -3.4 and -0.6,
thus for integer m,

-2+%3C=+m+%3C=+-1

This requirement for m contradicts the requirement that

matrix%281%2C3%2Cm+%3C=+-4%2C+or%2C+m+%3E=+0%29

Thus there are no solutions.

Edwin