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当xy/(x+y)=1/2,yz/(y+z)=1/3,zx/(z+x)=1/4时,...

郭敦顒回答: 已知xy/(x+y)=1,yz/(y+z)=2,zx/(z+x)=3, ∴1/x+1/y=1 (1),1/y+1/z=1/2 (2),1/x+1/z=1/3 (3) (1)-(2)得,1/x-1/z=1/2 (4) (3)+(4)得,2/x=5/6,x=12/5;代入(1)得5/12+1/y=1,y=12/7; (3)-(4)...

解方程组: x+y+zx = 1/2 ①, y+z+xy = 1/2 ②, z+x+yz = 1/2 ③. 顺次由①-②, ②-③, ③-①得: z-x = -x(y-z), x-y = -y(z-x), y-z = -z(x-y). ∴z-x = -x(y-z) = xz(x-y) = -xyz(z-x), 即(z-x)(1+xyz) = 0, ∴z-x = 0或1+xyz = 0. 1) 若z-x = 0, 有x-y = ...

已知 xy x+y =1, yz y+z =2, xz z+x =3,则: x+y xy =1,即 1 y + 1 x =1;(1) y+z yz = 1 2 ,即 1 y + 1 z = 1 2 ;(2) x+z xz = 1 3 ,即 1 x + 1 z = 1 3 .(3)(2)-(3)得到: 1 y - 1 x = 1 6 (4)(1)-(4)得到: 2 x = 5...

由已知 可以得出 xy=x+y (1) yz=2(y+z) (2) zx=3(z+x) (3) 由(3)得 z=3x/(x-3) (4) 由(1)得 y=x/(x-1) (5) 把(4)(5)代入(2) 解得 x=12/5

求点P(3,-1,2)到直线L: x+y-z+1=0,2x-y+z-4=0的距离. 解:x+y-z+1=0..........①;2x-y+z-4=0............② 令x=1;代入①②都得y-z=-2;因此可在直线L上取M(1,-2,0)和N(1,2,4)两点, 那么直线的方向数为{1-1,2+2,4-0}={0,4,4} 故直线L的标...

当x,y,z为正最小值是out[5].这是多元函数求极值,我用计算机算的,省的写步骤了。

1/x+1/(y+Z)=1/2 1/y+1/(x+z)=1/3 1/z+1/(x+y)=1/4 三个方程左边通分得 (x+y+z)/(x(y+z)=1/2 (x+y+z)/(y(x+z))=1/3 (x+y+z)/(z(x+y))=1/4 所以 x(y+z)=2(x+y+z) 方程1 y(x+z)=3(x+y+z) 方程2 z(x+y)=4(x+y+z) 方程3 方程1和方程...

xy/(x+y)=3 (1) yz/(y+z)=2 (2) xz/(x+z)=1 (3) from (1) xy = 3(x+y) y(x-3)= 3x y= 3x/(x-3) (4) sub (4) into (2) yz/(y+z)=2 [3xz/(x-3)] /[ 3x/(x-3) + z ] =2 3xz/[3x + z(x-3) ] =2 3xz = 6x +2z(x-3) xz +6z =6x z(x+6) =6x z= 6x/(x+6)...

拆分,1/(y+z)=1/y-1/z,以此类推,非常容易将三个方程式都拆分,可以得到解答,话说你是不是第三个式子打错了,应该是1/z+1/(x+z)=1/4吧,否则也太简单了

这个属于逻辑运算,逻辑运算时非零的数为真即为1 !(x+y)=0,(z-1)=1所以 !(x+y)+z-1=1 y+z/2=1 1和1做与运算的1,所以结果为1,n=1

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