二元一次方程~(5點)快~超易~!!!

若直線L_1: mx-ny=1 與 L_2: nx+my=7相交於(3,1),求m和n的值
3m-n=1----------1
3n+m=7---------2
____________
(1)x3+(2)
9m-3n+3n+n=3+7
10m=10
m=1
n=2

2011-02-16 22:53:23 補充：
3a-1/2b= 5 ......(1)
4a+5b= -16 ......(2)
__________
From1:
a=10b+1/3---------3
Sub. 3 into 2:
4(10b+1/3)+5b=-16
40b+4+15b=-48
b=-52/55
a=-31/11
_____________________________
2(x-4)+7y=0 -------1
9x+4y=0 -----------2
_________
From1:
y=(8-2x/7)---------3
Sub. 3 into 2:
9x+4(8-2x/7)=0
63x+32-8x=0
x=-32/55
y=72/55

1.3a-1/2b= 5 ......(1)
4a+5b= -16 ......(2)
Multiply equation by 2
6a - b = 10
multiply by 5
30a - 5b = 50 -------- (3)
4a+5b = -16 ......(2)
Add equation (2) from equation (3)
34a = 34
a = 1
3a- ½ b = 5
½ b = 3a - 5
b = 6a - 10
b = 6 - 10
b = -4

a = 1, b = - 4

2. 2(x-4)+7y=9x+4y=0
2x -8+7y =9x+4y = 0
9x – 2x +4y -7y + 8 = 0
7x – 3y + 8 = 0
7x = 3y – 8
x = (3/7)y – 8/7

3. 若直線L_1: mx-ny=1 與 L_2: nx+my=7相交於(3,1),求m和n的值
3m-1n = 1 與 L_2: 1n+3m =7
Solve two linear equations
3m -n = 1 -----------(1)
3n + m = 7 ----------- (2)
Multiply equation (1) by 3
9m -3n = 3 -----------(3)
Add equation (3) and equation (2)
10 m = 10
m = 1
n = 3m - 1
n = 3-1 = 2

m = 1 , n = 2

2011-02-16 23:35:31 補充：
Correction:
Sorry My question 2 is wrong. I didn't see the last part, = 0
2x + 7y - 8 = 0
9x + 4y = 0

2011-02-17 03:37:14 補充：
Question 2:
18x + 63 y - 72 = 0 --- (3)
18x + 8y = 0 ---- (4)
Equation (4) - (3)
55y - 72 = 0
y = 72/55
x = -8y/18
x = - 8(72)/18
x = - 32/55