快,加減聯合方程 20分

x+6y=19 ---(1)
x+2y=7 ---(2)
(1)-(2) 4y=12
y=3
x=1


9x-4y=56 ---(1)
3x-4y=40 ---(2)
(2)x3 9x-12y=120 ---(3)
(3)-(1) -8y = 64
y=-8
x=8/3

5p=1-q ---(1)
3p=7+q ---(2)
(1)+(2) 8p=8
p=1
q=6

3x=8y-4---(1)
3x=7y-2---(2)
(1)-(2) y=2
x=4

9p+4q+2=0---(1)
9p-2q-28=0---(2)
(1)-(2) 6q=-30
q=-5
p=2

3p-(q-10)=p-q=0
3p-(q-10)=0
3p-q=-10--(1)
p-q=0 --(2)
(1)-(2) 2p=-10
p=-5
q=-5

2013-01-05 22:03:33 補充：
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x+6y=19...1
x+2y=7...2
1-2
4y=12
y=3
Substituting this into 1
x+18=19
x=1


9x-4y=56...1
3x-4y=40...2

1-2
6x=16
x=3 over 8
Substituting this into 1
24-4y=56
-4y=32
y=-8


遲d再解

1. x+6y= 19 (1)
x+2y=7 (2)

(1)-(2) = 4y = 12
y = 3
sub y = 3 into (2)
x + 6 = 7
x = 1

2. 9x - 4y = 56 (1)
3x - 4y = 40 (2)

(1)-(2) = 6x = 16
x = 16/6
x = 8/3
sub x = 8/3 into (2)
3(3/8) - 4y = 40
8-4y =40
-4y = 32
y = -8

3. 5p = 1-q (1)
3p = 7+q (2)
(1)+(2)
8p = 8
p = 1

sub p=1 into (1)
5 = 1-q
q = -4

4. 3x = 8y -4 (1)
3x = 7y-2 (2)
(1)-(2)
0= y -2
y=2
sub y =2 into (1)
3x = 16-4
3x = 12
x = 4

5. 9p+4q+2 = 0 (1)
9p-2q-28= 0 (2)
(1)-(2)
6q+30=0
q = -5
sub q=-5 into 1
9p -20 +2 = 0
p = 2

6. 3p- (q-10) = p-q = 0
3p -(q-10) = 0 (1)
p-q = 0 (2)

(1) 3p-q =-10
(1)-(2)
2p = -10
p = -5

sub p = -5 into 2
-5-q = 0
q = -5