二元一次方程

(1)
7m + 4n = 18...........(1)
7m - 6n = 8 ............(2)
(1) - (2) we get
10n = 10
n = 1 and m = 2.
(2)
7x + 4y = 18xy
7(x/xy) + 4(y/xy) = 18
7/y + 4/x = 18 ...............(3)
7x - 6y = 8xy
7(x/xy) - 6(y/xy) = 8
7/y - 6/x = 8 .................(4)
Comparing (3) with (1) and (4) with (2), we get
1/y = m, so y = 1/m = 1/2.
1/x = n, so x = 1/n = 1.

(1)
7m+4n=18-------------(1)
7m-6n=8---------------(2)

(1)-(2):4n-(-6n)=18-8
10n=10
n=1
m=2

2)

利用(1)的結果解這題

7x+4y=18xy--------------(1)
7x-6y =8xy --------------(2)

(1)-(2):10y=10xy
x=1

Put x=1,
7+4y=18y
7=14y
y=0.5