先化简,后求值:x-y/x+3y - x^2-9y^2/x^2+6xy+9y^2 + 2y/x+3y,其中x=2,y=-3
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=(x-y)/(x+3y)-[(x+3y)(x-3y)/(x+3y)²]+2y/(x+3y)
=(x-y)/(x+3y)-(x-3y)/(x+3y)+2y/(x+3y)
=[(x-y)-(x-3y)+2y]/(x+3y)
=(x-y-x+3y+2y)/(x+3y)
=4y/(x+3y)
当x=2, y=-3时
原式=[4×(-3)]/[2+3×(-3)]
=-12/(-7)
=12/7
先化简,后求值:x-y\/x+3y - x^2-9y^2\/x^2+6xy+9y^2 + 2y\/x+3y,其中x=...
解：原式=(x-y)\/(x+3y)-(x²-9y²)\/(x²+6xy+9y²)+2y\/(x+3y)=(x-y)\/(x+3y)-[(x+3y)(x-3y)\/(x+3y)²]+2y\/(x+3y)=(x-y)\/(x+3y)-(x-3y)\/(x+3y)+2y\/(x+3y)=[(x-y)-(x-3y)+2y]\/(x+3y)=(x-y-x+3y+2y)\/(x+3y)=4y...
化简:x-y\/x+3y÷x^2-y^2\/x^2+6xy+9y^2-2y\/x+y
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
...x+3y) 2 +2(x+y)(x-y)-(x-2)(x+3),其中x=2,y=-3.
原式=（x+3y） 2 +2x 2 -2y 2 -x 2 -x+6=x 2 +9y 2 +6xy+2x 2 -2y 2 -x 2 -x+6=2x 2 +7y 2 +6xy-x+6当x=2，y=-3时，原式=2×2 2 +7×（-3） 2 +6×2×（-3）-2+6=8+63-36-2+6=39．
化简求值:根号x^-2xy+y^2 + x^2 -6xy+9y^2\/x-3y,其中x=根号3,y=根号5...
√x^-2xy+y^2 + x^2 -6xy+9y^2\/x-3y =√(x-y)^2+(x-3y)^2\/x-3y 由于y>x =y-x+x-3y =-2y =-2√5
计算:x²y-6xy+x+9y-3?
x^2y一6xy+x+9y一3 =(x^2y一6xy+9y)+(x一3)=y(x^2一6x+9)+(x一3)=y(x一3)^2+(x一3)=(x一3)[y(ⅹ一3)+1]=(x一3)(ⅹy一3y+1)。
...4y^2)÷(x-2y)-(4x^2-9y^2)÷(2x-3y),其中x=-4,y=1\/5
原式＝(x-2y)^2\/(x-2y)-(2x-3y)(2x+3y)\/(2x-3y)分式上下约分=x-2y-(2x+3y)=-x-5y 代入数值=-5
(x-3y)(x+3y)(x^2-9y^2)数学计算要过程
解：原式=（x^2-9y^2）（x^2-9y^2）=x^4-18x^2y^2+81y^4
...+x(x+2y³)-2(-x)²]÷3y²,其中x=1,y=3
[(x-3y)(x+3y)+x(x+2y³)-2(-x)²]÷3y²=(x²-9y²+x²+2xy³-2x²)÷3y²=(2xy³-9y²)÷3y²=2xy\/3-3 当x=1，y=3时 原式=2-3=-1
先化简再求值:3(2x+y)^2-2(x-2y)^2-4(x+3y)(x-3y)其中x=-2 y=-
打开括号，3(4x^2+y^2+4xy)-2(x^2+4y^2-4xy)-4(x^2-9y^2)= (12-2-4)x^2+(3-8+36)y^2+(12+8)xy =6x^2+31y^2+20xy 代入x，y值 =24+31+40 =95
先化简,再求值:(2x-3y)(2x+3y)-(y-2x) 2 +(x-y)(x+2y),其中 x=-2...
原式=4x 2 -9y 2 -（y 2 -4xy+4x 2 ）+x 2 +2xy-xy-2y 2 =4x 2 -9y 2 -y 2 +4xy-4x 2 +x 2 +2xy-xy-2y 2 =x 2 -12y 2 +5xy，当x=-2，y= 1 2 时，原式=4-12× 1 4 +5×（-2）× 1 2 =4-3-5=-4．
