kyotsu-test 2019 QI-Q1
Sign analysis of quadratic coefficients and expressions from a graph
Q1 For A $\sim$ K in the following sentences, choose the correct answer from among choices (0) $\sim$ (9) below. (1) Consider the quadratic function
$$y = a x ^ { 2 } + b x + c$$
whose graph is as shown in the figure at the right.
Then $a , b$ and $c$ satisfy the following expressions:
(i) $a \mathbf { A } 0 , b \mathbf { B } 0 , c \mathbf { C } 0$;
(ii) $a + b + c \mathbf { D } 0$;
(iii) $a - b + c \mathbf { E } 0$;
(iv) $4 a + 2 b + c \mathbf { F } 0$;
(v) $b ^ { 2 } - 4 a c \mathbf { G } 0$.
(2) Given the condition that $a , b$ and $c$ satisfy (i) and (ii) in (1), consider the case where the value of $a ^ { 2 } - 8 b - 8 c$ is minimized.
We see that $a = \mathbf { H }$. When we express $y = a x ^ { 2 } + b x + c$ in terms of $b$, we have
$$y = \mathbf { H } x ^ { 2 } + b x - b + \mathbf { I } \text {. }$$
Also, we see that the range of the values of $b$ is $\mathbf { J } < b < \mathbf { K }$. (0) 0
(1) 1
(2) 2
(3) 3
(4) 4
(5) - 2 (6) - 4 (7) $>$ (8) $=$ (9) $<$