请你解答一下图片中的第七题---Question 7:
(江西·高考真题) 当 a > 0, b > 0 时, 不等式 -b < 1/x < a 的解是 ( )
A. x < -1/b 或 x > 1/a
B. -1/a < x < 1/b
C. x < -1/a 或 x > 1/b
D. -1/b < x < 0 或 0 < x < 1/a
Handwritten Annotations for Question 7:
∵a>0, b>0 ∴ -b<0, a>0.
-b < 1/x < a
-b < 1/x 且 1/x < a
∵a>0, b>0
1/x > -b => 1/x + b > 0 => (1+bx)/x > 0
If x > 0, 1+bx > 0 => bx > -1 => x > -1/b. Combined with x > 0, gives x > 0.
If x < 0, 1+bx < 0 => bx < -1 => x > -1/b. Combined with x < 0, gives -1/b < x < 0.
So, -b < 1/x solution is x > 0 or -1/b < x < 0 which simplifies to x < -1/b or x > 0 (My previous analysis was incorrect for the negative case). Let's re-evaluate the handwritten annotations.
Handwritten says:
-b < 1/x => 1/x > -b
If x > 0, 1 > -bx => bx > -1. Since b > 0, x > -1/b. Combined with x > 0, gives x > 0. (This seems wrong based on the subsequent steps in the annotation).
Let's follow the annotation steps carefully.
-b < 1/x:
If x > 0: -bx < 1 => bx > -1 => x > -1/b. Since x > 0, this is x > 0.
If x < 0: -bx > 1 => bx < -1. Since b > 0, x < -1/b. Combined with x < 0, this is x < -1/b.
So, -b < 1/x solution is x < -1/b or x > 0. This matches the first part of the handwritten annotation conclusion below.
1/x < a:
If x > 0: 1 < ax => x > 1/a. Since a > 0, 1/a > 0. Combined with x > 0, this is x > 1/a.
If x < 0: 1 > ax => x < 1/a. Since x < 0, this is x < 0.
So, 1/x < a solution is x > 1/a or x < 0. This matches the second part of the handwritten annotation conclusion below.
Handwritten annotation conclusion steps:
∴ -b < 1/x => x < -1/b 或 x > 0
∴ 1/x < a => x > 1/a 或 x < 0
To solve -b < 1/x < a, we need the intersection of these two solution sets.
Intersection of (x < -1/b or x > 0) and (x > 1/a or x < 0).
Let S1 = (-∞, -1/b) U (0, +∞)
Let S2 = (-∞, 0) U (1/a, +∞)
S1 ∩ S2 = [(-∞, -1/b) U (0, +∞)] ∩ [(-∞, 0) U (1/a, +∞)]
= [(-∞, -1/b) ∩ (-∞, 0)] U [(-∞, -1/b) ∩ (1/a, +∞)] U [(0, +∞) ∩ (-∞, 0)] U [(0, +∞) ∩ (1/a, +∞)]
Since -1/b < 0 and 1/a > 0:
= (-∞, -1/b) U ∅ U ∅ U (1/a, +∞)
= (-∞, -1/b) U (1/a, +∞)
This corresponds to x < -1/b or x > 1/a.
This matches Option A. The handwritten annotation's final check mark is on A.
Question 8:
(2023·全国·高考真题) 已知集合 M = {-2, -1, 0, 1, 2}, 集合 N = {x|x^2 - x - 6 >= 0}, 则 M ∩ N = ( )
A. {-2, -1, 0, 1}
B. {0, 1, 2}
C. {-2}
D. {2}
Handwritten Annotations for Question 8:
x^2 - x - 6 >= 0
(x-3)(x+2) >= 0
x <= -2 或 x >= 3
N = (-∞, -2] U [3, +∞)
M = {-2, -1, 0, 1, 2}
M ∩ N = {-2} (Implicitly derived from M and N)