代數不等式(急~20分)

1.
4 < 5 + x
5 + x > 4
5 + x - 5 > 4 - 5
x > -1


2.
8 < 3x + 20
3x + 20 > 8
3x + 20 - 20 > 8 - 20
3x > - 12
3x/3 > -12/3
x > -4


3.
4(x + 7) > 2(x + 15)
4x + 28 > 2x + 30
4x + 28 - 2x - 28 > 2x + 30 - 2x - 28
2x > 2
2x/2 > 2/2
x > 1


4.
5(x - 2) - 3(3x + 1) ≥ 0
5x - 10 - 9x - 3 ≥ 0
-4x - 13 ≥ 0
-4x - 13 + 13 ≥ 0 + 13
-4x ≥ 13
-4x/(-4) ≤ 13/(-4)
x ≤ -13/4


1.
-(2/5)x > -6
-(2/5)x x (-5/2) < -6 x (-5/2)
x < 15


2.
(1/4)(5 - x) > 3
4 x (1/4)(5 - x) > 4 x 3
5 - x > 12
5 - x - 5 > 12 - 5
-x > 7
-x(-1) < 7(-1)
x < 7


3.
(1 - 4x)/15 - (9 - x)/10 ≤ 0
30(1 - 4x)/15 - 30(9 - x)/10 ≤ 0
2(1 - 4x) - 3(9 - x) ≤ 0
2 - 8x - 27 + 3x ≤ 0
-25 - 5x ≤ 0
-25 - 5x + 25 ≤ 0 + 25
-5x ≤ 25
-5x/(-5) ≤ 25/(-5)
x ≥ -5


4.
(3x/2) + 1 > 5 - (x/2)
(3x/2) + 1 + (x/2) - 1 > 5 - (x/2) + (x/2) - 1
2x > 4
2x/2 > 4/2
x > 2
=