X-y=16000,(1 20%)X-(1 10%)Y=25000怎样解?

x>=1,x-y y=x-1(x x+x+x+y=20 x+x+y=14 x=?y=? y=20x X（1-x)的最大值? 求导 y=[x/(1+x)]^x 1=x+y 2=20x+30y y'-(1/x)y=xe^-x 1/(x+y)-1/(x-y)=-3/20,2/(x+y)+3/(y-x)=-(1/5)急啊! 集合N=｛（x,y)|（x-1）^2｝+(y-1)^20},M={(x,y)|x^2+y^2 已知x y为实数,且（x+y)(x+y+1)=20 求x+y的值 请问60%x+20%y=30%(x+y) 怎么得到x:y=1:3 x>0,y>0 2x+5y=20 1/x+1/y的最大值 z=0.015x*x+y*x*0.05+(1-x-y)*2.5*(x+y) x>0.35.xy>0.70x+y 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 x.y都是自然数,且x(x-u)-y(y-x)+12,求x.y得值快1且x(x-y)-y(y-x)=12 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 y'/y=1/x X-y=16000,(1 20%)X-(1 10%)Y=25000怎样解?