求y=x^3-19x-30的导数

7-x+y-(y-x)=7-(x-y)+(x-y)……（这步添括号,y-x=-(x-y),代入x-y=3）=7-3+3=77^2=49（7的平方等于49）

2X+3Y=18（1）3X+2Y=19（2）（1）×2得4x+6y=36(3)(2)×3得9x+6y=57(4)(4)-(3)得5x=21x=4.2代入（1）得8.4+3y=18y=3.2

2/3

(2x-y)/(x+y)=3所以(x+y)/(2x-y)=1/3原式=1/2*(2x-y)/(x+y)+1/3*(x+y)/(2x-y)=3/2+1/9=29/18

解原式=2(x-y)/(x+y)-(x+y)/3(x-y)=6(x-y)(x-y)/[3(x+y)(x-y)]-(x+y)x+y)/[3(x-y)(x+y)]=5(x-y)(x-y)/[(x+y)(x

x+2y=3(1)x-y=-2(2)消去y,(1)+(2)×2得：x+2x=3-43x=-1x=-1/3消去x,(1)-(2)得：2y+y=3+23y=5y=5/3方程组的解为x=-1/3,y=5/3

=x+y×2.5

参考不知道对不对x-y=6得x-y的平方=36x-y的平方等于x平方+y平方-2xy所以116--2xy＝36所以-2xy＝-80所以xy就等于40

可以得出x.x+y.y-6x-8y+25=x.x-6x+9+y.y-8y+16=(x-3).(x-3)+(y-4).(y-4)=0因为(x-3).(x-3)>=0,(y-4).(y-4)>=0所以x=

∵2x-y/x+2y=3∴2(2x-y)/x+2y-9(x+2y)/2x-y+3＝2×3-9×1/3+3=6

答案是2.4x-2y/x+3y=(2x-y/x+3y)乘以2=4,4x+12y/2x-y=(x+3y/2x-y)乘以4=1/2x4=2,所以代数式等于4-2=2.

x+y分之x-y=2求x+y分之3x-3y减x-y分之2(x+y)的值x+y分之x-y=2x-y=2(x+y)(x+y)分之(3x-3y)-(x-y)分之2(x+y)的值x+y分之3x-3y=(x+y

x+y分之x-y=2x-y=2(x+y)求x+y分之3x-3y=(x+y)分之3(x-y)=(x+y)分之6(x-y)=6-x-y分之2(x+y)=-(x+y)分之2(x+y)=-2

x²+y²=19(x+y)²=x²+y²+2xy=25xy=3(x-y)*(x-y)=(x-y)²=x²+y²-2xy=

2x-y\x+y=32x-y=3(x+y)2x-y=3x+3y3x-2x=-y-3yx=-4y2x-y/2x+2y+x+y/6x-3y=(-8y-y)/(-8y+2y)+(-4y+y)/(-24y-3

若x-y/x+y=5则x-y=5(x+y)所以求x-y/2x+2y+5x+5y/3x-3y=5(x+y)/[2(x+y)]+5(x+y)/3(x-y)=5/2+5(x+y)/[3*5(x+y)]=5/

2乘以2+3分之一乘以二分之一=4+6分之1=6分之25

(x-2y)/(x+2y)=3取倒数(x+2y)/(x-2y)=1/3所以原式=(1/3)[(x-2y)/(x+2y)]-3[(x+2y)/(x-2y)]=(1/3)×3-3×(1/3)=0

绝对值项恒非负,两绝对值项之和=0,两绝对值项分别=03x-y=0(1)x+y=0(2)(1)+(2)4x=0x=0,代入(2)y=-x=0(x-y)/(xy)无意义,因此题目错了.

X=3+Y,将其带入X+Y=7也就是3+Y+Y=7,Y=5带入X-Y=3也就是X-5=3,X=8所以X的平方+Y的平方=X乘以X+Y乘以Y=8乘以8+5乘以5=64+25=89x的平方+y的平方=89