The problem is about a quadratic function $y = ax^2 + bx + c$ and its graph. We need to determine the signs of $a$, $b$, and $c$ based on the graph, and then use the given equations to find the values of $a$, $c$ in terms of $b$. Finally, we need to find the range of possible values for $b$ when $a^2 - 8b - 8c$ is minimized.
2025/4/7
1. Problem Description
The problem is about a quadratic function and its graph. We need to determine the signs of , , and based on the graph, and then use the given equations to find the values of , in terms of . Finally, we need to find the range of possible values for when is minimized.
2. Solution Steps
(1)
(i) Since the parabola opens downwards, . The graph intersects the y-axis at a positive value, so .
Since the axis of symmetry is on the positive side of y-axis, . Since , this implies .
So, is (9), is (7), and is (7).
(ii) The problem says
Thus, is (0)
(iii) The problem says
Thus, is (0)
(iv) The image does not give enough information to solve this equation.
(v) The image does not give enough information to solve this equation.
(2) From (i) and (ii), we have:
Subtracting the second equation from the first, we get , so . However, we found that in part (1), and therefore, we cannot use the equation directly.
Since the problem mentions (i), we use , , and . From (ii) and (iii), we have and . Thus , so , and .
This means our initial assessment was wrong.
We have and . Then or .
Then .
Since , .
Since , .
Thus , so , which implies or .
If , we have or . Then .
The value is minimized when , so .
Then .
However, we need to express in terms of . If , then , and , so .
Since , and and , we consider the function .
Since , we have .
Substituting for , we have .
The minimum of occurs when , so .
Then is (6).
.
Since , we have , so .
Therefore, .
Thus, is (4).
Also . Since and , , and , so . This is not correct.
The vertex must be , so . Since , we have , or .
Since , we have .
Since , . , , so . Since , , so .
Therefore .
is (0), and is (4).
3. Final Answer
A: (9)
B: (7)
C: (7)
D: (0)
E: (0)
F: Don't Know
G: Don't Know
H: (6)
I: (4)
J: (0)
K: (4)