（10y-3x)/(3x-y)=2
10y-3x=6x-2y
9x=12y
y=3x/4
（（15-8y）^(1/2))/（（5x+4y）^(1/2))
=[(15-8y)/(5x+4y)]^(1/2)
=[(15-6x)/(8x)]^(1/2)
15-6x>=0
x