For an integer n, the inequality
x^2 + nx + 15 < -89 - 3x^2
has no real solutions in $x$. Find the number of different possible values of $n$.
First, let's move all terms to one side and simplify. We have
\(4x^2 + nx + 104 < 0 \)
Let's set this up as an equation. We have
\(4x^2 + nx + 104 = 0\)
This will have real solutions when
\(n^2 - 4 (4) (104) ≥ 0 \\ n^2 ≥ 1664\)
\(n ≥ 40.79 \\ n ≤ -40.79\)
This is when there is a real value. Which means that when
\( n < 40.79 \\ n > -40.79\)
there will be no real solutions. Thus, we have
\( n = [ -40 , 40 ] \)
There are 81 values of n.
Thus our answer is 81 !
Thanks! :)
\(x^2 + nx + 15 < -89 - 3x^2\)
so i first brought everything to the left side to get \(4x^2 + nx + 104 < 0\)
then i divided by 4 to get\(x^2 + \frac{n}{4}x + 26 < 0\)
for x to have no real solutions the discriminant must be negative
so \(\frac{n^2}{16}-4(26)\) must be negative. the less than sign is useless since smaller right hand values make c greater
the greatest value of n that works is 40
but we also can have negatives, least of which is -40
so -40 to 40 is \(\boxed{81}\) numbers