數學!!教我做

1) 3x －　2y = 7 ------------ (1)
x + 2y = 5 ------------ (2)
(1) + (2), 4x = 12
x = 3
3 + 2y = 5
y = 1
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2) 4x － 5y = 23 ------------ (1)

5x +3y =1 ------------ (2)
(1) * 3, 12x － 15y = 69 ------------ (3)
(2) * 5, 25x +15y =5 ------------ (4)
(3) + (4), 37x = 74
x = 2
5(2) +3y =1
y = -3
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不等色:

1) 6x － 12 ＞ 3x
6x ＞ 3x + 12
3x ＞ 12
x > 4
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2) 4x － 3 ＞ 10
4x ＞ 13
x > 13/4
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3) 3(5x－1) ＜2 ( 2x－7 )
15x－3 ＜4x－14
11x－3 ＜14
11x ＜17
x < 17/11
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4) 3x－2(1－x) ≦4 ( 2x+3 )
3x－2 + 2x ≦ 8x+12
－2 ≦ 3x+12
－14 ≦ 3x
x >= -14/3
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1) 3x-2y=7--------------[1]
x+2y=5---------------[2]
[1]+[2],
4x=12
x=3#
將x=3代入[2],
(3)+2y=5
y=1#
∴x=3,y=1#

2008-01-02 17:00:50 補充：
2) [1]x3 3(4x-5y)=23x3 2x-15y=69------------[3] [2]x5 5(5x+3y)=5 25x+15y=5-----------[4] [3]+[4] (12x-15y)+(25x+15y)=74 37x=74 x=2 將x=2代入[2] 5(2)+3y=1 y=-3

1)3x-2y=7...........(1)
x+2y=5...............(2)
(1)+(2)
3x-2y+x+2y=7+5
4x=12
x=3....................(3)
sub(3) into (2)
(3)+2y=5
2y=2
y=1
thereforex=3,y=1.

2)4x-5y=23.............(1)
5x+3y=1................(2)
3(1)+5(2)
12x-15y+25x+15y=69+5
37x=74
x=2.......................(3)
sub (3) into (2)
5(2)+3y=1
3y=-9
y=-3
therefore,x=2,y=-3

1)6x-12&gt;3x
6x-3x&gt;12
3x&gt;12
x&gt;4

2)4x-3&gt;10
4x&gt;13
x&gt;13/4

3)3(5x-1)&lt;2(2x-7)
15x-3&lt;4x-14
11x&lt;-11
x&lt;-1

4)3x-2(1-x)&lt;=4(2x+3)
3x-2+2x&lt;=8x+12
5x-2&lt;=8x+12
-3x&lt;=14
x&gt;=-14/3