+821 For what values of x is y=f(x) negative?
f(x) = 2x^2 - 13x + 20 - 5x^2 + 19x + 7.
Enter your answer as an interval or a union of separated intervals.
+130466 f(x) = -3x^2 -6x + 27
Set to 0 to find the roots
-3x^2 -6x + 27 = 0
3x^2 + 6x -27 = 0
3 (x^2 + 2x - 9) = 0
x^2 + 2x - 9 = 0
x^2 + 2x = 9 complete the square on x
x^2 + 2x + 1 = 9 + 1
(x + 1)^2 = 10
x + 1 = sqrt 10 or x + 1 = -sqrt 10
x = sqrt 10 -1 or x = -sqrt 10 - 1
Negative on
(inf , -sqrt (10 ) - 1 ) U (sqrt (10) -1, inf )
