Answer:
f(x) = 9 + 9x - x² - x³
f'(x) = 9 - 2x - 3x²
3x² + 2x - 9 = 0
x = (-2 ± √(2² - 4(3)(-9)))/(2(3))
= (-2 ± √(4 + 108))/6
= (-2 ± √112)/6
= (-2 ± 4√7)/6
= (-1 ± 2√7)/3
f((-1 - 2√7)/3) = -5.049
f((-1 + 2√7)/3) = 16.901
When -6 < k < 17, f(x) will have one real solution.
a = 17, b = -6
