Answer:
Because the graph has the parabol shape, so the equation of it has the function:
y = ax² + bx + c
Because the parabol has a peak at point (0; 9)
=> 9 = a.0² + b.0 + c
=> c = 9
=> The parabol has a function:
y = ax² + bx + 9
Because the parabol goes through point (3; 0)
=> 0 = a.3² + b.3 + 9
=> 9a + 3b = - 9 (1)
Because the parabol goes through point (-3; 0)
=> 0 = a.(- 3)² + b.(- 3) + 9
=> 9a - 3b = - 9 (2)
Plus (1) and (2):
=> 18.a = - 18
=> a = - 1
Substitute the result on (1)
=> b = 0
=> The function of the parabol: y = - x² + 9
=> a = - 1
=> Choose A. - 1
