二元一次方程...

1.2x+5y=47------(1)
4y=3x+10------(2)
From(2),4y-3x=10
(1)x3
6x+15y=141-------------(3)
(2)x2
8y-6x=20-----------------(4)
(3)+(4):
6x+15y+8y-6x=141+20
23y=161
y=7



2008-02-21 22:56:56 補充：
Put y=7 into (1)2x+5(7)=472x+35=472x=12x=6so x=6, y=7

2008-02-21 23:03:17 補充：
(b)由此,或用其他方法,求下列聯立方程中a和b的值.2a+5b=47ab---(1)4b=3a+10ab---(2)From(2),4b-3a=10ab(1)x3:6a+15b=141ab--------(3)(2)x2:8b-6a=20ab--------------(4)(3)+(4):6a+15b+8b-6a=141ab+20ab23b=161abb=7ab1=7aa=1/7

2008-02-21 23:03:38 補充：
b=1/6

a) 2x+5y=47 (1)
4y=3x+10 (2)
由(2), 3x-4y=-10 (3)
3(1)-2(3) 15y-(-8y)=141-(-20)
23y=161
y=7
把y=7 放入(3) 3x-28=-10
3x=18
x=6
b) 把a=1/y b=1/x 以重寫公式
得出 2/y+5/x =47/xy
和 4/x=3/y+10/xy
把兩條式通分母,得出和a)一樣的兩條式
表示 a=1/7 b=1/6

y = 3x/4 + 2.5
2x + 5(3x/4) + 2.5 x 5 = 47
5.75 x = 34.5
x = 6
y = 7

4b - 10ab = 3a
b (4 - 10a) = 3a
b = 3a/(4 - 10a)
2a + 15a/(4 - 10a) = 47a x 3a/(4 - 10a)
2a (4 - 10a) + 15a = 141 a^2
8a - 20 a^2 + 15a = 141 a^2
161a^2 - 23a = 0
7a^2 - a = 0
a = 0 or 1/7
b = 0 or 1/6