數學功課吾識做3(請盡快回答)

1.
2x + y = 2........(1)
y = x - 1..........(2)

把 (2) 代入 (1),
2x + (x - 1) = 2
3x - 1 = 2
3x = 3
x = 1

代入 (2) 可得 y = 1 - 1 = 0

{ x = 1
{ y = 0

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2.
2x + 3y = 5.....(1)
x + y = 5.......(2)

從 (2) 可得 y = 5 - x ...... (3)
代入 (1):
2x + 3(5 - x) = 5
2x + 15 - 3x = 5
-x = -10
x = 10

代入 (3) 得 y = 5 - 10 = -5

{ x = 10
{ y = -5

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3.
3x + y = 13.....(1)
x - y = 3........(2)

從 (2) 可得 y = x - 3 ...... (3)
代入 (1):
3x + (x - 3) = 13
4x - 3 = 13
4x = 16
x = 4
代入 (3) 得 y = 4 - 3 = 1

{ x = 4
{ y = 1


2015-01-09 22:28:07 補充：
同學，為何你在 2015-01-05 發問的兩個帖都刪除了？

我估計這個帖應該不會被刪吧？

1.2x+y=2........(1)
y=x-1..........(2)
Sub(2)into(1)
2x+(x-1)=2
3x-1=2
3x=3
x=1
Sub x=1 into(2)
y=1-1
y=0
So, x=1, y=0

2.2x+3y=5.....(1)
x+y=5.......(2)
From(2),
x=5-y.....(3)
Sub(3)into(1)
2(5-y)+3y=5
10-2y+3y=5
y=-5
Sub y=-5 into(3)
x=5-(-5)
x=10
So, x=10, y=-5

3.3x+y=13.....(1)
x-y=3........(2)
From(2),
x=3+y.....(3)
Sub(3)into(1)
3(3+y)+y=13
9+3y+y=13
4y=4
y=1
Sub y=1 into(3)
x=3+1
x=4
So, x=4, y=1

乖乖呀~前車可鑑喲^已付出的^不要去追究吧//
你不明白甚麼叫...[功成身退]...?
但...那人不是你==

1.
2x+y=2........(1)
y=x-1..........(2)
代(2)入(1)
2x+x-1=2
3x=3
x=1
代x=1入(2)
y=1-1
y=0
所以(x,y)=(1,0)

2.
2x+3y=5.....(1)
x+y=5.......(2)
由(2),
y=5-x.......(3)
代(3)入(1)
2x+3(5-x)=5
2x+15-3x=5
-x=-10
x=10
代x=10入(3)
y=5-10
y=-5
所以(x,y)=(10,-5)

3.
3x+y=13.....(1)
x-y=3........(2)
由(1),
y=13-3x........(3)
代(3)入(1)
x-13+3x=3
4x=16
x=4
代x=4入(3)
y=13-3*4
y=1
所以(x,y)=(4,1)