{超急!!} 數學數學數學(10分)

1). y=3x+5......(1)
y=2x+3......(2)
將 (1) 代入(2)
y=2x+3
3x+5=2x+3
3x-2x=3-5

x=-2

將x=-2 代入(1)
y=3x+5
y=3(-2)+5

y=1


2).x-y= - 3......(1)
x+y=1......(2)
(1)x-y= - 3
x=y-3......(3)
將 (3) 代入(2)
x+y=1
(y-3)+y=1
2y=4

y=2

將y=2 代入(1)
x-y= - 3
x-2=-3

x=-1

3). x+3y=5......(1)
x+2y=3......(2)
(1)x+3y=5
x=5-3y......(3)
將 (3) 代入(2)
x+2y=3
(5-3y)+2y=3
-y=-2

y=2

將y=2 代入(1)
x+3y=5
x+3(2)=5

x=-1

4). 2x+y=2......(1)
x-y= - 3......(2)
(1)2x+y=2
y=2-2x......(3)
將 (3) 代入(2)
x-y= - 3
x-(2-2x)=-3
3x=5

x=5/3

將x=5/3 代入(1)
2x+y=2
2(5/3)+y=2

y=3/5

5). b-4a=3......(1)
3a+b= - 11......(2)
(1) b-4a=3
b=4a+3......(3)
將 (3) 代入(2)
3a+b= - 11
3a+(4a+3)= - 11
7a=-14

a=-2

將a=-2代入(1)
b-4a=3
b-4(-2)=3
b+8=3

b=-5

6). 2a+3b=10......(1)
4a-b=6......(2)
(2)4a-b=6
4a-6=b......(3)
將 (3) 代入(1)
2a+3(4a-6)=10
2a+12a-18=10
14a=28

a=2

將a=2代入(1)
2a+3b=10
2(2)+3b=10
3b=6

b=2

1)

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

(1) - (2)

y - y = ( 3x + 5 ) - ( 2x + 3 )

0 = 3x - 2x + 5 - 3

0 = x + 2

0 - 2 = x + 2 - 2

-2 = x

x = -2

y = 2 x -2 + 3

y = -4 + 3

y = -1
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2)

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

(1) + (2)

( x - y ) + ( x + y ) = -3 + 1

2x = -2

2x ÷ 2 = -2 ÷ 2

x = -1

-1 + y = 1

-1 + y + 1 = 1 + 1

y = 2

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3)

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

(1) - (2)

( x + 3y ) - ( x + 2y ) = 5 - 3

x - x + 3y - 2y = 2

y = 2

x + 2 x 2 = 3

x + 4 = 3

x + 4 - 4 = 3 - 4

x = -1

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4)

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

(1) + (2)

( 2x + y ) + ( x - y ) = 2 + ( -3 )

2x + x + y - y = 2 - 3

3x = -1

3x ÷ 3 = -1 ÷ 3

x = - ( 1/3 )

- ( 1/3 ) - y = -3

- [ - ( 1/3 ) - y ] = - ( -3 )

( 1/3 ) + y = 3

( 1/3 ) + y - ( 1/3 ) = 3 - ( 1/3 )

y = ( 8/3 )

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5)

b-4a=3......(1)
3a+b= - 11......(2)

(1) - (2)

( b - 4a ) - ( 3a + b ) = 3 - ( -11 )

b - b - 4a - 3a = 3 + 11

-7a = 14

-7a ÷ 7 = 14 ÷ 7

-a = 2

- ( -a ) = - ( +2 )

a = -2

b - ( 4 x -2 ) = 3

b - ( -8 )

b + 8 = 3

b + 8 - 8 = 3 - 8

b = -5

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6)

2a+3b=10......(1)
4a-b=6......(2)

(1) x 2

2 ( 2a + 3b ) = 2 x 10

4a + 6b = 20 ...... (3)

(3) - (2)

( 4a + 6b ) - ( 4a - b ) = 20 - 6

4a - 4a + 6b - b = 14

5b = 14

5b ÷ 5 = 14 ÷ 5

b = 2.8

4a - 2.8 = 6

4a - 2.8 + 2.8 = 6 + 2.8

4a = 8.8

4a ÷ 4 = 8.8 ÷ 4

a = 2.2

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1).2x+3=3x+5
x=-2

2)x=y-3
x+y=y-3+y=1
y=2
x=-1

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

4)x=y-3
2x+y=2(y-3)+y=3y-6=2
y=8/3=2.6666667
x=8/3-3=-1/3=-0.3333333

5)b=3+4a
3a+b=3a+3+4a=-11
7a+3=-11
a=-2
b=3+4(-2)=-5

6)2a+3b=10
4a+6b=20
4a=20-6b
4a-b=20-6b-b=6
7b=14
b=2
2a+3(2)=10
a=2

1.x=-2,y=-1
2.x=-1,y=2
3.x=-1,y=2
4.x=-1/3,y=8/3
5.x=-2,y=-5
6.x=2,y=2