已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?

来源：学生作业帮助网 编辑：六六作业网 时间：2024/11/18 08:15:29
已知x/y=2/7则x^2-3xy+2y^2/2x^2-3xy+7y^2=?1/x+1/y=2求2x-3xy+2y/3x+3y+2xy=?已知x/y=2/7则x^2-3xy+2y^2/2x^2-3xy

已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?
已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?
已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?
1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?

已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?已知x/y=2/7 则x^2-3xy+2y^2 / 2x^2-3xy+7y^2=?1/x+1/y=2 求2x-3xy+2y / 3x+3y+2xy=?
1,(x^2-3xy+2y^2) / (2x^2-3xy+7y^2)
=(x-2y)(x-y)/[(2x-y)(x-y)+6y^2],
由x/y=2/7,得：7x=2y,
所以x-y=-5y/7,x-2y=-12y/7,2x-y=-3y/7,
所以原式=[(-12y/7)(-5y/7)]/[(-3y/7)(-5y/7)+6y^2]
=(60/49)/[(15/49)+6]
=60/309=20/103.
或(x^2-3xy+2y^2) / (2x^2-3xy+7y^2) （分子,分母同除以y^2）
=[(x/y)^2-3(x/y)+2]/[2(x/y)^2-3(x/y)+7]
=[(2/7)^2-3*2/7+2]/[2*(2/7)^2-3*2/7+7]
=[4/49-6/7+2]/[8/49-6/7+7]
=(60/49)/(309/49)=20/103.
2,由1/x+1/y=2,得：x+y=2xy,
所以(2x-3xy+2y) / (3x+3y+2xy)
=[2(x+y)-3xy]/[3(x+y)+2xy]
=[4xy-3xy]/[6xy+2xy]
=xy/(8xy)=1/8.

由x/y=2/7可得，x=2/7y，代入式子=（4/49-6/7+2）y2/(8/49-6/7+7)y2=20/103
由1/x+1/y=2 得x+y=2xy代入式子=(4xy-3xy)/(6xy+2xy)=1/8

第一题.另x=2.y=7.得解为20/103

已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 已知x-y=8 xy=7,则3xy-2x+2y+4(y-x)²=? 已知x+xy+y=3,则(3x+2xy+3y)/(2x+xy+2y)= 已知x-y=3xy,则2x+3xy-2y除以x-2xy-y=? 已知x-y=3xy,则2x+3xy-2y/x-2xy-y= 已知xy/x+y=1/2,则代数式3x-5xy+3y/-x+3xy-y= 已知xy^2=-2求xy（2x^3y^7+5x^2y 已知x/y=3/4 ,则3xy-2y/2x+4xy=? 已知x+y=6,xy=-3,则x^2y+xy^2=? 已知x+y=5,xy=-3,则x^2y+xy^2, 已知x+y=2,xy=3,则x²+y²-3xy=? 已知x+y=6,xy=-3,则x∧y+xy∧2= 已知x=3y,试求（x-y)^2+2xy-y^2/x^2+7xy+y^2 已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 已知xy/x+y=2,则代数式3x-5y+8y/-x+3xy-y的值 已知x+y=1,xy=-2,则x²y+xy²-2xy 已知x^2-3xy+2y^2=0 则x/y+x/y= 已知(x+y)/(x-y)=3/2,则(x²+y²)/xy =