Question

若Y分之X=二分之一,求X的平方+2XY+Y的平方 除以 X的平方-XY-2 Y^2

Answer 1

因为 x/y=1/2 所以 x=y/2 y=2x

所以：

(x^2+2xy+y^2)/ (X^2-xy-2 y^2)

=（x+y)(x+y)/(x+y)(x-2y)

=(x+y)/(x-2y)

把 y=2x 代进 (x+y)/(x-2y)

则：

(x+y)/(x-2y)

=(x+2x)/(x-4x)

=3x/(-3x)

=-3/3

=-1