3y²6x÷21x²-搜答案-搜搜考试网

解因为X+6Y=21所以X=21-6Y带入3X+8Y=51后得到63-18Y+8Y=51所以Y=1.2带入后X=13.8

1.（x-1)^2+2(1-x)=(x-1)(x-1-2)=(x-1)(x-3)2.(x-y)/(x+3y)÷(x^2-y^2)/(x^2+6xy+9y^2)-2y/(x+y）=(x-y)/(x+3y

原式=(x²+4xy+4y²-3x²-2xy+y²-5y²)÷2x=(-2x²+2xy)÷2x=-x+y再问：x=-2y=二分之一再答：=5

由(1)得3x+3y+2x-2y=365x+y=36(3)由(2)得4x+4y-3x+3y=-20x+7y=-20(4)(3)×7-(4)得34x=272∴x=8把x=8代入(3)得y=-4∴x=8y

{(x+y)/2+(x-y)/3=63(x+y)+2(x-y)=36(1)4(x+y)-3(x-y)=-20(2)由（1）*3+(2)*2得9(x+y)+6(x-y)+8(x+y)-6(x-y)=36

(x—y)^7÷(y—x)^6+(—x—y)^3÷(x+y)^2=x-y-(x+y)=-2y

(x+2y)(3x-5y)-(6x⁴y²-2x²y²）÷（2x²y²）=(x+2y)(3x-5y)-2x²y²(3x&

3x^2(x-y)+6x(y-x)=3x^2(x-y)-6x(x-y)=(x-y)(3x^2-6x)=3x(x-y)(x-2)

先化简,合并同类项,化简结果是(-5/2)x,然后把x=-2带入,结果等于5

解题思路：对于这种等式一定可以化成平方相加的形式，这里面要使用到完全平方公式。解题过程：

（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y=（x+y)（x-y)-y^2+（x-y)^2-2y（3x^2-xy)÷2y=（x+y)（x-y)-y^2+（x-y)^2

(2x+y)(x-3y)=2x(x-3y)+y(x-3y);y(x-3y)+y(x+3y)=2xy;所以2x(x-3y)+2xy=2x(x-3y+y)=2x(x-2y);2x(x-2y)÷(2x)=x

解题思路：本题目应该是9y的平方吧，要不然没法做出来。解题过程：(2x-6y)/(x的平方-9y)=2(x-3y)/[(x-3y)(x+3y)]=2/(x+3y)=2/3

[(x-y)/(x+3y)]/[(x^2-y^2)/(x^2+6xy+9y^2)]-xy/(x+y)=(x-y)/(x+3y)*(x+3y)^2/(x-y)(x+y)-xy/(x+y)=(x+3y)/

原式=(x-y)/(x+3y)×[(x+3y)^2/(x+y)(x-y)]-2y/(x+y)=(x+3y)/(x+y)-2y/(x+y)=(x+3y-2y)/(x+y)=(x+y)/(x+y)=1

6x(x-y)^2+3(y-x)^3=6x(x-y)^2-3(x-y)^3=3(x-y)^2[2x-(x-y)]=3(x-y)^2(x+y)

(x-y)^7÷(y-x)^6+(-x-y)^3÷(x+y)^2=(x-y)^7÷(x-y)^6+[-(x+y)^3]÷(x+y)^2=(x-y)+[-(x+y)]=x-y-x-y=-2y

:【(2x-y)(2x+y)+y(y+6x)】÷2x=（4x^2-y^2+y^2+6xy)÷2x=2x+3yx^2代表的是x的平方的意思

很累-3x-2y