Question

二元一次方程...

Answer 1

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 补充： Put y=7 into (1)2x+5(7)=472x+35=472x=12x=6so x=6
y=7 2008-02-21 23:03:17 补充： (b)由此
或用其他方法
求下列联立方程中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 补充： 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 以重写公式 得出 2/y+5/x =47/xy 和 4/x=3/y+10/xy 把两条式通分母
得出和a)一样的两条式 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