若x分之y=7分之2,求x的平方+2xy+y的平方分之x的平方-y的平方=?
问题描述：
若x分之y=7分之2,求x的平方+2xy+y的平方分之x的平方-y的平方=?
答
x^2-y^2/x^2+2xy+y^2
=(x+y)(x-y)/(x+y)^2
=x-y/x+y
因为y/x=2/7
所以x+y不=0
原式=5/9
答
x的平方+2xy+y的平方分之x的平方-y的平方=(x-y)(x+y)/(x+y)^2=(x-y)/(x+y),把y=2/7x带入，得(x-y)/(x+y)=5/9
答
y/x=2/7
(x^2-y^2)/(x^2+2xy+y^2)
=(x+y)(x-y)/(x+y)^
=(x-y)/(x+y)
上下同除x
=(1-y/x)/(1+y/x)
=(1-2/7)/(1+2/7)
=5/9
答
y/x=2/7
2x=7y
x=7y/2
x的平方+2xy+y的平方分之x的平方-y的平方
=(x+y)(x-y)/(x+y)^2
=(x-y)/(x+y)
=(5y/2)/(9y/2)
=5/9